I'll sign off now. Thanks for your company and congratulations to Celtic on reaching the last four in the Scottish Cup. Ronny Deila's men meet Inverness CT at Hampden next month, with Championship rivals Hibernian and Falkirk squaring up in the other tie.
We'll be back for more live action on Friday night when Motherwell take on Lanarkshire rivals Hamilton in the Premiership. Join us for that one, if you can.
Join the debate at #bbcscotfootball
MBEHAN: "Great victory for Celtic but the stupidity from Stokes will leave Deila unhappy #bbcscotfootball"
Paul Black: "Cruising to the treble. Ronny Deila's the man! #TrebleWinners #bbcscotfootball"
Jim Simpson: "#bbcscotfootball D.Utd just not good enough, needed to keep the two in Jan! Not gonna score in mth of Sundays!"
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In League Two, Albion Rovers were 2-0 winners at Arbroath, with Gary Fisher adding to Ali Love's first-half goal.
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Can anyone stop the Celtic juggernaut this season? Aberdeen can go level on points with the Premiership leaders if they win at Dens Park on Saturday lunchtime but Ronny Deila's men have played a game less and will be action against United almost as soon as that one is over.
Inverness Caley Thistle have history against Celtic in the Scottish Cup and they turned them over in the league back in August.
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More from Simon Donnelly on BBC Radio Scotland
"We showed a bit of courage to keep the ball in their half at the start of the second half but then the second goal goes in and effectively kills the game. They were soft goals from our perspective."
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Dundee United assistant manager Simon Donnelly
"I don't think the three games have been particularly dirty, the reaction of the Celtic players maybe influences the referee's decision (on Ryan McGowan's late red card), but I'd need to see it again."
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Celtic manager Ronny Deila on BBC Radio Scotland
"It was a great performance and an important victory. We showed that we have a tempo that is very hard to cope with.
"The league is the most important thing and we want another three points on Saturday."
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Just how many red cards will we get when these two go head-to-head again on Saturday? That's six dismissals in three games now, although two of those were later overturned. Crazy!
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I'm not sure Dundee United will be looking forward to coming back to Celtic Park on Saturday. Jackie McNamara's men have now gone seven games without a win - and to make matters worse former stars Gary Mackay-Steven and Stuart Armstrong will be available to play against them.
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That's three in a row for these sides, with Celtic enjoying the upper hand, winning this one and last Sunday's League Cup final after a draw at Tannadice. And guess what? They meet again on Saturday on Premiership duty.
FULL-TIME
Celtic 4-0 Dundee United
Celtic stroll into the last four of the Scottish Cup and the treble dream for manager Ronny Deila is alive and well. Jason Denayer, Leigh Griffiths, Kris Commons and Virgil van Dijk got the goals in a one-sided affair.
GOAL
Celtic 4-0 Dundee United (Van Dijk)
Dundee United are all over the place as Celtic centre-backs Jason Denayer and Virgil van Dijk combine for the latter to knock the ball home.
YELLOW CARDS
We have a wee sprinkling of yellow cards as well, with Celtic pair John Guidetti and Emilio Izaguirre cautioned for their reactions to Ryan McGowan's daft lunge.
RED CARD
Now it's getting silly as Ryan McGowan catches Liam Henderson with a hefty challenge and the Dundee United defender will also trudge off for an early bath.
RED CARD
A sour end to the night for Celtic forward Anthony Stokes, who lashes out with an elbow at Paul Paton after taking umbrage at a challenge from Ryan McGowan.
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We're into the last five minutes as Celtic substitute John Guidetti fires a shot over the top.
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BBC Scotland's Tom English at Celtic Park
"Kris Commons gets his 12th goal of the season. The guy is a machine. Celtic must have been in some kind of trance when they thought about not giving him the deal he was looking for. One of the best Celtic signings in modern times."
YELLOW CARD
A frustrating night for Nadir Ciftci takes another wrong turn as the Dundee United striker picks up a booking.
SUBSTITUTION
Once again, the goalscorer is withdrawn immediately as Kris Commons receives a warm round of applause and Liam Henderson gets a taste of the action.
GOAL
Celtic 3-0 Dundee United (Commons)
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Moments after missing a great chance in front of goal, Kris Commons makes amends with a classy, clipped finish from John Guidetti's pass.
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Calum Butcher connects well with a shot from 20 yards after a nice passage of play from Dundee United but the ball flies right into the arms of goalkeeper Craig Gordon.
SUBSTITUTION
Final switch for the visitors as Aidan Connolly replaces fellow 19-year-old Blair Spittal. A few boos from the home crowd for the newcomer, who won a contentious penalty in the first tie at Tannadice.
SUBSTITUTION
Celtic make a change at right-back, with Darnell Fisher taking the place of Efe Ambrose.
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Henri Anier is involved in a United attack straight but can't quite find the racing Blair Spittal with his pass into the penalty area.
SUBSTITUTION
Henri Anier and Charlie Telfer are on for Dundee United, with Chris Erskine and Ryan Dow making way.
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Kris Commons lays off a free-kick for Anthony Stokes to have a crack and Radoslaw Cierzniak has to get down smartly to push the ball away.
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BBC Sportsound pundit Willie Miller
"Nadir Ciftci needed to perform tonight for Dundee United to have a chance but he has not reached the standards he is capable of."
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United started the second half in sprightly fashion but that Leigh Griffiths strike has knocked the stuffing out of them. Can the visitors regroup, go again and get a goal to make this one interesting again?
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Virgil van Dijk strides forward from central defence into the inside left channel as Celtic seek a third goal but United get enough bodies in the way.
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BBC Scotland's Tom English at Celtic Park
"That's what the home fans wanted - the assurance goal. Gorgeous delivery from Scott Brown and close-range volley from Leigh Griffiths. Against the run of play, but this thing is done now. I'll eat my hat if it's not. Not that I have a hat."
SUBSTITUTION
Not much time for Leigh Griffiths to enjoy that goal as he is withdrawn and John Guidetti will lead the Celtic attack for the remainder of the evening.
GOAL
Celtic 2-0 Dundee United (Griffiths)
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Celtic double their lead as Leigh Griffiths watches a long, curling ball from Scott Brown drop over his shoulder and aims a smart volley into the corner of the net.
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BBC Scotland's Tom English at Celtic Park
"Dundee United are gaining momentum and Celtic have really lost any sense of urgency. The hosts are asking for trouble if they continue to allow United to set the tempo."
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There's another clumsy foul from Efe Ambrose, who has already been cautioned, on Nadir Ciftci. After that reprieve, the Celtic defender heads the resulting free-kick away to safety.
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Ryan McGowan powers forward to reach a Chris Erskine pass but the full-back's strong cross finds no takers. Nadir Ciftic then curls in an awkward delivery and Craig Gordon gathers well.
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James Forrest skips forward to cause more problems for the United defence only for Leigh Griffiths and Kris Commons to get in the way of each other in the penalty box.
KICK-OFF
We are up and running again...
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Dundee United are still in this game at just 1-0 down but they will need to really up their game after the interval to put the hosts under pressure. Celtic were in cruise control for that first 45 minutes.
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The BBC Radio Scotland team are discussing the early booking for Dundee United keeper Radoslaw Cierzniak for clattering into Leigh Griffiths outside the penalty area.
"It was borderline," says Tom English. "It was an assassination!" splutters an incredulous Willie Miller.
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LEAGUE TWO LATEST
There's one other match being played in Scotland tonight and Albion Rovers lead 1-0 at Arbroath at half-time thanks to an early goal from Ali Love.
HALF-TIME
Celtic 1-0 Dundee United
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It's been all Celtic in this Scottish Cup quarter-final replay and the home side lead thanks to Jason Denayer's 17th-minute header.
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Jason Denayer is in the mood for another goal as he surges forward from defence. The ball breaks to Kris Commons and the playmaker's dinked effort is gathered by Radoslaw Cierzniak.
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Nir Bitton is suddenly one-on-one with Radoslaw Cierzniak but the Celtic midfielder is not often in these situations and makes a horrible mess of it, losing out to covering defender Callum Morris.
YELLOW CARD
Celtic defender Efe Ambrose is cautioned for a clumsy late challenge. Half-time will be upon us soon.
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Dundee United full-back Ryan McGowan powers forward to fire in a good cross and home keeper Craig Gordon gets a vital touch, with Nadir Ciftci in close proximity. The United striker ends up in the net feeling sorry for himself and is therefore not alert to the loose ball.
HITS THE WOODWORK
Celtic winger James Forrest has the beating of John Rankin every time and his latest run and cross has Radoslaw Cierzniak flapping to palm the ball against the crossbar.
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BBC Scotland's Tom English at Celtic Park
"Celtic's possessions stats would be off the scale, but they wouldn't want to leave themselves open to a sucker punch. United don't look capable of it at the moment, but this tie is still not over despite Celtic's ownership of the ball. Nadir Ciftci's effort, though easily saved by Craig Gordon, might serve as a reminder to the home team that they're not in the clear just yet."
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Dundee United finally have a shot on target as Nadir Ciftci goes for a very ambitious drive from fully 35 yards out. Easy save for Craig Gordon.
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Yet another Celtic corner as James Forrest takes aim at goal and his shot is deflected wide by stand-in left-back John Rankin on the slide. Virgil van Dijk gets his head on the delivery but can't keep it down.
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United survive another couple of Celtic corners but the visitors have not been able to retain any kind of possession so far.
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Celtic striker Leigh Griffiths has another crack at goal and this one draws a few oohs and aaahs from the crowd as it whistle over from 25 yards.
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BBC Sportound pundit Murdo MacLeod
"The Dundee United heads are down, it just looks like they are accepting what is happening to them."
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BBC Radio Scotland's match commentator Rob Maclean
"Whenever Celtic lose the ball, they work so quickly to get it back."
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BBC Scotland's Tom English at Celtic Park
"Anthony Stokes doesn't score many goals these days but that was a precise free-kick right on to Jason Denayer's head for the opener. United defending awful, though. Denayer unmarked and barely had to jump. Routine stuff. United haven't turned up yet. Celtic extremely comfortable."
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Celtic winger James Forrest has a dig from long range and it takes an awkward bounce in front of goal but Radoslaw Czerniak is right behind it. Leigh Griffiths is next to have a pop and his effort is well wide.
GOAL
Celtic 1-0 Dundee United (Denayer)
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Anthony Stokes curls in a juicy delivery from a free-kick and Celtic defender Jason Denayer has a free run to flick a looping header over Radoslaw Czerniak.
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Celtic striker Leigh Griffiths produces an acrobatic flick to get on the end of a driven cross from Anthony Stokes but can only divert the ball straight into the arms of Radoslaw Czerniak.
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Better from the visitors now as Nadir Ciftci draws a foul from Efe Ambrose but Paul Paton's over-hit free-kick has Calum Butcher at full-stretch to get his head on it and Craig Gordon gathers comfortably.
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United full-back Ryan McGowan shows great strength and determination to get forward and drill in a cross but Celtic keeper Craig Gordon is alive to the danger.
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BBC Scotland's Tom English at Celtic Park
"Jackie McNamara's heart would have skipped a beat when Radoslaw Czerniak clattered into Leigh Griffiths in the opening minute. Red has so often been the colour in this this fixture in recent weeks. Yellow this time. Celtic dominant. Kris Commons has 11 goals this season and looks determined to get number 12 tonight."
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Kris Commons is at the heart of everything for Celtic as he lets fly with a shot that whizzes high over the crossbar. Not one of his best but he did have a few similar early 'sighters' before opening the scoring at Hampden on Sunday.
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Celtic are ramping up the early pressure, with a series of dangerous crosses and corners, United are rattled but hanging on.
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"It's got be a red card," BBC Sportsound pundit Murdo MacLeod.
YELLOW CARD
Kris Commons slips a pass through to Leigh Griffiths and the Celtic striker is wiped out by Radoslaw Cierzniak a few yards from the penalty box after knocking the ball past the keeper. Much to everyone's surprise at Celtic Park United man is shown a yellow rather than red card.
KICK-OFF
We are off at Celtic Park...
Join the debate at #bbcscotfootball
Paul Black on Twitter: #bbcscotfootball looking forward to seeing Commons play the number 10 role, where he belongs."
tom and 20 others: "Celtic will have the tactical advantage. Their tactic of buyin up the opposition's best players usually gives them the edge #bbcscotfootball"
Post update
Not long to go now. Just a reminder that Inverness Caley Thistle will face the winners of this replay in the Scottish Cup semi-finals. Falkirk and Hibernian meet in the other game at Hampden. The order of those ties will be revealed tomorrow.
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BBC Radio Scotland's Tom English
"I give Dundee United more of chance tonight because Nadir Citfci is back and he can cause problems but I still think Celtic will be too strong."
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United were toothless in attack at Hampden but that should change since striker Nadir Ciftci is back from his League Cup suspension and avoided sanction in this contest after a review of his involvement in the melee that saw Virgil van Dijk and Paul Paton sent for early baths. Earlier this week, manager Jackie McNamara said he thought the Turkish-born forward was "the best player in Scotland", with the "on his game" proviso.
And Ciftci will need to be on it tonight since it has been 23 years since United won at Celtic Park.
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Celtic midfielder Stefan Johansen was the man-of-the-match at Hampden on Sunday but he is banned for tonight's game following two bookings in the contest. That's a big blow since the Norwegian midfielder must the front-runner for Scotland's player of the year.
The hosts are also without Gary Mackay-Steven and Stuart Armstrong who are cup-tied but those two will finally get the chance to face their former club on league duty this Saturday.
Well, the Scottish Football Association and Scottish Professional Football League say such proposals are "impractical" and could undermine their own efforts to increase supporter involvement.
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ONE DOWN...
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Celtic lifted the League Cup on Sunday. Will they go on to make it a clean sweep or can Dundee United revenge their defeat at Hampden and progress to the last four in Scottish Cup?
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Dundee United manager Jackie McNamara on BBC Radio Scotland
"It's a tough match. We have not won here for a long time. We need everyone to have a strong performance and hopefully we can cause an upset. It's great to have Nadir Ciftci back but left-back is a problem for us and John Rankin will fill in there for us."
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BBC Sportsound pundit Willie Miller
"Tonight is a great night for Kris Commons to make a statement. If he wants to say anything about playing in his preferred central position this is his chance."
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Sean Dillon let his side down with a reckless lunge near the halfway line and he misses out tonight, along with full-back Paul Dixon, who was sent off in the first Scottish Cup meeting at Tannadice for stopping a shot with his arm in front of goal. Radoslaw Cierzniak saved the resulting penalty in the 1-1 draw.
Two others were sent off early in the first tie, with Virgil van Dijk winning an appeal against his red card and poor Paul Paton also having his overturned since he wasn't even involved in the argy-bargy.
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Celtic landed the first trophy in what they hope will be a domestic clean sweep when they won 2-0 at Hampden on Sunday in the League Cup final. United were doughty in defence but seldom caused their opponents any trouble and their cause was lost when skipper Sean Dillon was sent off 10 minutes into the second half when they were already trailing.
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Celtic manager Ronny Deila on BBC Radio Scotland
"Stefan Johansen is an important player for us but we have Kris Commons switching to the number 10 role and he scored 35 goals last season, so I'm not worried.
"We have a dream and the players know what we are fighting for [the domestic treble].
"We want to do this in 90 minutes but we have to be prepared for everything."
Quiet on set! It's Celtic v Dundee United take three. And, action... Yes, this is the third instalment of four consecutive matches between the sides and by the end of the night Inverness CT will know who they are playing in the Scottish Cup semi-finals.
Live Reporting
Colin Moffat
All times stated are UK
Get involved
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Latest PostPost update
I'll sign off now. Thanks for your company and congratulations to Celtic on reaching the last four in the Scottish Cup. Ronny Deila's men meet Inverness CT at Hampden next month, with Championship rivals Hibernian and Falkirk squaring up in the other tie.
We'll be back for more live action on Friday night when Motherwell take on Lanarkshire rivals Hamilton in the Premiership. Join us for that one, if you can.
Join the debate at #bbcscotfootball
MBEHAN: "Great victory for Celtic but the stupidity from Stokes will leave Deila unhappy #bbcscotfootball"
Paul Black: "Cruising to the treble. Ronny Deila's the man! #TrebleWinners #bbcscotfootball"
Jim Simpson: "#bbcscotfootball D.Utd just not good enough, needed to keep the two in Jan! Not gonna score in mth of Sundays!"
Post update
In League Two, Albion Rovers were 2-0 winners at Arbroath, with Gary Fisher adding to Ali Love's first-half goal.
Post update
Can anyone stop the Celtic juggernaut this season? Aberdeen can go level on points with the Premiership leaders if they win at Dens Park on Saturday lunchtime but Ronny Deila's men have played a game less and will be action against United almost as soon as that one is over.
Inverness Caley Thistle have history against Celtic in the Scottish Cup and they turned them over in the league back in August.
Post update
More from Simon Donnelly on BBC Radio Scotland
"We showed a bit of courage to keep the ball in their half at the start of the second half but then the second goal goes in and effectively kills the game. They were soft goals from our perspective."
Post update
Dundee United assistant manager Simon Donnelly
"I don't think the three games have been particularly dirty, the reaction of the Celtic players maybe influences the referee's decision (on Ryan McGowan's late red card), but I'd need to see it again."
Post update
Celtic manager Ronny Deila on BBC Radio Scotland
"It was a great performance and an important victory. We showed that we have a tempo that is very hard to cope with.
"The league is the most important thing and we want another three points on Saturday."
Post update
Just how many red cards will we get when these two go head-to-head again on Saturday? That's six dismissals in three games now, although two of those were later overturned. Crazy!
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I'm not sure Dundee United will be looking forward to coming back to Celtic Park on Saturday. Jackie McNamara's men have now gone seven games without a win - and to make matters worse former stars Gary Mackay-Steven and Stuart Armstrong will be available to play against them.
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That's three in a row for these sides, with Celtic enjoying the upper hand, winning this one and last Sunday's League Cup final after a draw at Tannadice. And guess what? They meet again on Saturday on Premiership duty.
FULL-TIME
Celtic 4-0 Dundee United
Celtic stroll into the last four of the Scottish Cup and the treble dream for manager Ronny Deila is alive and well. Jason Denayer, Leigh Griffiths, Kris Commons and Virgil van Dijk got the goals in a one-sided affair.
GOAL
Celtic 4-0 Dundee United (Van Dijk)
Dundee United are all over the place as Celtic centre-backs Jason Denayer and Virgil van Dijk combine for the latter to knock the ball home.
YELLOW CARDS
We have a wee sprinkling of yellow cards as well, with Celtic pair John Guidetti and Emilio Izaguirre cautioned for their reactions to Ryan McGowan's daft lunge.
RED CARD
Now it's getting silly as Ryan McGowan catches Liam Henderson with a hefty challenge and the Dundee United defender will also trudge off for an early bath.
RED CARD
A sour end to the night for Celtic forward Anthony Stokes, who lashes out with an elbow at Paul Paton after taking umbrage at a challenge from Ryan McGowan.
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We're into the last five minutes as Celtic substitute John Guidetti fires a shot over the top.
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BBC Scotland's Tom English at Celtic Park
"Kris Commons gets his 12th goal of the season. The guy is a machine. Celtic must have been in some kind of trance when they thought about not giving him the deal he was looking for. One of the best Celtic signings in modern times."
YELLOW CARD
A frustrating night for Nadir Ciftci takes another wrong turn as the Dundee United striker picks up a booking.
SUBSTITUTION
Once again, the goalscorer is withdrawn immediately as Kris Commons receives a warm round of applause and Liam Henderson gets a taste of the action.
GOAL
Celtic 3-0 Dundee United (Commons)
Moments after missing a great chance in front of goal, Kris Commons makes amends with a classy, clipped finish from John Guidetti's pass.
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Calum Butcher connects well with a shot from 20 yards after a nice passage of play from Dundee United but the ball flies right into the arms of goalkeeper Craig Gordon.
SUBSTITUTION
Final switch for the visitors as Aidan Connolly replaces fellow 19-year-old Blair Spittal. A few boos from the home crowd for the newcomer, who won a contentious penalty in the first tie at Tannadice.
SUBSTITUTION
Celtic make a change at right-back, with Darnell Fisher taking the place of Efe Ambrose.
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Henri Anier is involved in a United attack straight but can't quite find the racing Blair Spittal with his pass into the penalty area.
SUBSTITUTION
Henri Anier and Charlie Telfer are on for Dundee United, with Chris Erskine and Ryan Dow making way.
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Kris Commons lays off a free-kick for Anthony Stokes to have a crack and Radoslaw Cierzniak has to get down smartly to push the ball away.
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BBC Sportsound pundit Willie Miller
"Nadir Ciftci needed to perform tonight for Dundee United to have a chance but he has not reached the standards he is capable of."
Post update
United started the second half in sprightly fashion but that Leigh Griffiths strike has knocked the stuffing out of them. Can the visitors regroup, go again and get a goal to make this one interesting again?
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Virgil van Dijk strides forward from central defence into the inside left channel as Celtic seek a third goal but United get enough bodies in the way.
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BBC Scotland's Tom English at Celtic Park
"That's what the home fans wanted - the assurance goal. Gorgeous delivery from Scott Brown and close-range volley from Leigh Griffiths. Against the run of play, but this thing is done now. I'll eat my hat if it's not. Not that I have a hat."
SUBSTITUTION
Not much time for Leigh Griffiths to enjoy that goal as he is withdrawn and John Guidetti will lead the Celtic attack for the remainder of the evening.
GOAL
Celtic 2-0 Dundee United (Griffiths)
Celtic double their lead as Leigh Griffiths watches a long, curling ball from Scott Brown drop over his shoulder and aims a smart volley into the corner of the net.
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BBC Scotland's Tom English at Celtic Park
"Dundee United are gaining momentum and Celtic have really lost any sense of urgency. The hosts are asking for trouble if they continue to allow United to set the tempo."
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There's another clumsy foul from Efe Ambrose, who has already been cautioned, on Nadir Ciftci. After that reprieve, the Celtic defender heads the resulting free-kick away to safety.
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Ryan McGowan powers forward to reach a Chris Erskine pass but the full-back's strong cross finds no takers. Nadir Ciftic then curls in an awkward delivery and Craig Gordon gathers well.
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James Forrest skips forward to cause more problems for the United defence only for Leigh Griffiths and Kris Commons to get in the way of each other in the penalty box.
KICK-OFF
We are up and running again...
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Dundee United are still in this game at just 1-0 down but they will need to really up their game after the interval to put the hosts under pressure. Celtic were in cruise control for that first 45 minutes.
Post update
The BBC Radio Scotland team are discussing the early booking for Dundee United keeper Radoslaw Cierzniak for clattering into Leigh Griffiths outside the penalty area.
"It was borderline," says Tom English. "It was an assassination!" splutters an incredulous Willie Miller.
Post update
LEAGUE TWO LATEST
There's one other match being played in Scotland tonight and Albion Rovers lead 1-0 at Arbroath at half-time thanks to an early goal from Ali Love.
HALF-TIME
Celtic 1-0 Dundee United
It's been all Celtic in this Scottish Cup quarter-final replay and the home side lead thanks to Jason Denayer's 17th-minute header.
Post update
Jason Denayer is in the mood for another goal as he surges forward from defence. The ball breaks to Kris Commons and the playmaker's dinked effort is gathered by Radoslaw Cierzniak.
Post update
Nir Bitton is suddenly one-on-one with Radoslaw Cierzniak but the Celtic midfielder is not often in these situations and makes a horrible mess of it, losing out to covering defender Callum Morris.
YELLOW CARD
Celtic defender Efe Ambrose is cautioned for a clumsy late challenge. Half-time will be upon us soon.
Post update
Dundee United full-back Ryan McGowan powers forward to fire in a good cross and home keeper Craig Gordon gets a vital touch, with Nadir Ciftci in close proximity. The United striker ends up in the net feeling sorry for himself and is therefore not alert to the loose ball.
HITS THE WOODWORK
Celtic winger James Forrest has the beating of John Rankin every time and his latest run and cross has Radoslaw Cierzniak flapping to palm the ball against the crossbar.
Post update
BBC Scotland's Tom English at Celtic Park
"Celtic's possessions stats would be off the scale, but they wouldn't want to leave themselves open to a sucker punch. United don't look capable of it at the moment, but this tie is still not over despite Celtic's ownership of the ball. Nadir Ciftci's effort, though easily saved by Craig Gordon, might serve as a reminder to the home team that they're not in the clear just yet."
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Dundee United finally have a shot on target as Nadir Ciftci goes for a very ambitious drive from fully 35 yards out. Easy save for Craig Gordon.
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Yet another Celtic corner as James Forrest takes aim at goal and his shot is deflected wide by stand-in left-back John Rankin on the slide. Virgil van Dijk gets his head on the delivery but can't keep it down.
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United survive another couple of Celtic corners but the visitors have not been able to retain any kind of possession so far.
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Celtic striker Leigh Griffiths has another crack at goal and this one draws a few oohs and aaahs from the crowd as it whistle over from 25 yards.
Post update
BBC Sportound pundit Murdo MacLeod
"The Dundee United heads are down, it just looks like they are accepting what is happening to them."
Post update
BBC Radio Scotland's match commentator Rob Maclean
"Whenever Celtic lose the ball, they work so quickly to get it back."
Post update
BBC Scotland's Tom English at Celtic Park
"Anthony Stokes doesn't score many goals these days but that was a precise free-kick right on to Jason Denayer's head for the opener. United defending awful, though. Denayer unmarked and barely had to jump. Routine stuff. United haven't turned up yet. Celtic extremely comfortable."
Post update
Celtic winger James Forrest has a dig from long range and it takes an awkward bounce in front of goal but Radoslaw Czerniak is right behind it. Leigh Griffiths is next to have a pop and his effort is well wide.
GOAL
Celtic 1-0 Dundee United (Denayer)
Anthony Stokes curls in a juicy delivery from a free-kick and Celtic defender Jason Denayer has a free run to flick a looping header over Radoslaw Czerniak.
Post update
Celtic striker Leigh Griffiths produces an acrobatic flick to get on the end of a driven cross from Anthony Stokes but can only divert the ball straight into the arms of Radoslaw Czerniak.
Post update
Better from the visitors now as Nadir Ciftci draws a foul from Efe Ambrose but Paul Paton's over-hit free-kick has Calum Butcher at full-stretch to get his head on it and Craig Gordon gathers comfortably.
Post update
United full-back Ryan McGowan shows great strength and determination to get forward and drill in a cross but Celtic keeper Craig Gordon is alive to the danger.
Post update
BBC Scotland's Tom English at Celtic Park
"Jackie McNamara's heart would have skipped a beat when Radoslaw Czerniak clattered into Leigh Griffiths in the opening minute. Red has so often been the colour in this this fixture in recent weeks. Yellow this time. Celtic dominant. Kris Commons has 11 goals this season and looks determined to get number 12 tonight."
Post update
Kris Commons is at the heart of everything for Celtic as he lets fly with a shot that whizzes high over the crossbar. Not one of his best but he did have a few similar early 'sighters' before opening the scoring at Hampden on Sunday.
Post update
Celtic are ramping up the early pressure, with a series of dangerous crosses and corners, United are rattled but hanging on.
Post update
"It's got be a red card," BBC Sportsound pundit Murdo MacLeod.
YELLOW CARD
Kris Commons slips a pass through to Leigh Griffiths and the Celtic striker is wiped out by Radoslaw Cierzniak a few yards from the penalty box after knocking the ball past the keeper. Much to everyone's surprise at Celtic Park United man is shown a yellow rather than red card.
KICK-OFF
We are off at Celtic Park...
Join the debate at #bbcscotfootball
Paul Black on Twitter: #bbcscotfootball looking forward to seeing Commons play the number 10 role, where he belongs."
tom and 20 others: "Celtic will have the tactical advantage. Their tactic of buyin up the opposition's best players usually gives them the edge #bbcscotfootball"
Post update
Not long to go now. Just a reminder that Inverness Caley Thistle will face the winners of this replay in the Scottish Cup semi-finals. Falkirk and Hibernian meet in the other game at Hampden. The order of those ties will be revealed tomorrow.
Post update
BBC Radio Scotland's Tom English
"I give Dundee United more of chance tonight because Nadir Citfci is back and he can cause problems but I still think Celtic will be too strong."
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United were toothless in attack at Hampden but that should change since striker Nadir Ciftci is back from his League Cup suspension and avoided sanction in this contest after a review of his involvement in the melee that saw Virgil van Dijk and Paul Paton sent for early baths. Earlier this week, manager Jackie McNamara said he thought the Turkish-born forward was "the best player in Scotland", with the "on his game" proviso.
And Ciftci will need to be on it tonight since it has been 23 years since United won at Celtic Park.
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Celtic midfielder Stefan Johansen was the man-of-the-match at Hampden on Sunday but he is banned for tonight's game following two bookings in the contest. That's a big blow since the Norwegian midfielder must the front-runner for Scotland's player of the year.
The hosts are also without Gary Mackay-Steven and Stuart Armstrong who are cup-tied but those two will finally get the chance to face their former club on league duty this Saturday.
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A quick aside, with some breaking news. You may have seen our earlier story on MSPs backing plans to allow fans the right to buy their football clubs.
Well, the Scottish Football Association and Scottish Professional Football League say such proposals are "impractical" and could undermine their own efforts to increase supporter involvement.
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ONE DOWN...
Celtic lifted the League Cup on Sunday. Will they go on to make it a clean sweep or can Dundee United revenge their defeat at Hampden and progress to the last four in Scottish Cup?
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Dundee United manager Jackie McNamara on BBC Radio Scotland
"It's a tough match. We have not won here for a long time. We need everyone to have a strong performance and hopefully we can cause an upset. It's great to have Nadir Ciftci back but left-back is a problem for us and John Rankin will fill in there for us."
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BBC Sportsound pundit Willie Miller
"Tonight is a great night for Kris Commons to make a statement. If he wants to say anything about playing in his preferred central position this is his chance."
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Sean Dillon let his side down with a reckless lunge near the halfway line and he misses out tonight, along with full-back Paul Dixon, who was sent off in the first Scottish Cup meeting at Tannadice for stopping a shot with his arm in front of goal. Radoslaw Cierzniak saved the resulting penalty in the 1-1 draw.
Two others were sent off early in the first tie, with Virgil van Dijk winning an appeal against his red card and poor Paul Paton also having his overturned since he wasn't even involved in the argy-bargy.
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Celtic landed the first trophy in what they hope will be a domestic clean sweep when they won 2-0 at Hampden on Sunday in the League Cup final. United were doughty in defence but seldom caused their opponents any trouble and their cause was lost when skipper Sean Dillon was sent off 10 minutes into the second half when they were already trailing.
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Celtic manager Ronny Deila on BBC Radio Scotland
"Stefan Johansen is an important player for us but we have Kris Commons switching to the number 10 role and he scored 35 goals last season, so I'm not worried.
"We have a dream and the players know what we are fighting for [the domestic treble].
"We want to do this in 90 minutes but we have to be prepared for everything."
LINE-UPS FROM CELTIC PARK
Celtic: Gordon, Ambrose, Denayer, van Dijk, Izaguirre, Biton, Brown, Forrest, Commons, Stokes, Griffiths. Subs: Guidetti, Scepovic, Zaluska, Wakaso, Fisher, McGregor, Henderson.
Dundee Utd: Cierzniak, McGowan, Fojut, Morris, Rankin, Spittal, Paton, Butcher, Erskine, Dow, Ciftci. Subs: Souttar, Telfer, Connolly, Scott Smith, Szromnik, Anier, Spark.
Referee: Calum Murray
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Quiet on set! It's Celtic v Dundee United take three. And, action... Yes, this is the third instalment of four consecutive matches between the sides and by the end of the night Inverness CT will know who they are playing in the Scottish Cup semi-finals.