Match ends, Dundee 1, Dundee United 4.
Dundee United went top of the Scottish Premiership table after ending city rivals Dundee's unbeaten record in comprehensive fashion.
Mario Bilate's penalty gave the visitors a first-half advantage.
Ryan Dow doubled their lead after the break, then headers by Callum Morris and Keith Watson made it 4-0.
Dundee's Thomas Konrad was sent off after receiving his second booking before Greg Stewart scored an injury-time consolation for the hosts.
That, though, could not prevent United moving above Inverness at the top of the division on goals scored.
Paul Hartley's men will have a chance for revenge in the League Cup at Tannadice on Wednesday but must improve on their performance in the 127th league meeting of the sides if they are to record their first derby win in a decade.
Jackie McNamara's side had lost just once - against Celtic - and were three points clear of their neighbours ahead of the first of two meetings in four days.
But Dundee had the better of the frantic opening exchanges, settling quicker and passing the ball with real purpose.
Yet it was United who had the better chances as Dow's header drew a save from Kyle Letheren and Chris Erskine drove a shot wide from distance.
As the early pace dropped, the visitors began to enjoy more possession and Dundee defender James McPake had to clear a Gary Mackay-Steven cross from under the crossbar.
Yet the lively Mackay-Steven would make a more decisive contribution soon afterwards by winning a penalty kick. Paul Paton did the groundwork by winning the ball in midfield and allowing Mackay-Steven to burst into the box, where he was clumsily challenged by defender Konrad.
Referee Steven McLean pointed to the spot and booked the German stopper before Bilate tucked the ball into Letheren's bottom right-hand corner.
Dundee lifted the tempo in the wake of that setback and had a good look at the United goal when Gary Harkins picked out the onrushing Philip Roberts superbly at the far post, but the former Arsenal youth player drilled his effort narrowly wide.
The hosts were full of energy and endeavour at the start of the second period, with playmaker Paul McGowan coming into the game much more.
But their hopes were hampered by another self-inflicted wound.
This time United's John Rankin robbed Jim McAlister of possession in the final third and Dow drifted into the box before skidding the ball low past Letheren.
A third goal soon followed, Morris getting ahead of Konrad at the near post to flick a teasing Paton free-kick into the net for his first goal for the club.
Watson then made a brilliant last-ditch block to deny Harkins before popping up in the other box to score the fourth goal, nodding in at the back post from another Paton free-kick.
Substitute Blair Spittal dragged a shot just wide as United tried to heighten the misery for the home support, with the boisterous away support chanting, "We want five".
Dundee defender Konrad headed up the tunnel a few minutes before his team-mates after his challenge on Scott Smith earned him a second yellow and a red.
But Stewart did give the home fans who had not headed for the exits something to cheer in stoppage time when he arrowed a fine left-footed shot past Radoslaw Cierzniak.
- 4KonradBooked at 90mins
- 14RobertsSubstituted forTankulicat 57'minutes
- 29HarkinsSubstituted forWightonat 66'minutes
- 11FerrySubstituted forBoyleat 75'minutes
- 15StewartBooked at 71mins
- 12WatsonBooked at 73mins
- 17ErskineBooked at 40minsSubstituted forS Armstrongat 58'minutes
- 6PatonBooked at 45minsSubstituted forSmithat 81'minutes
- 18DowBooked at 54mins
- 19BilateSubstituted forSpittalat 67'minutes
- 10S Armstrong
- Steven McLean
- Shots on Target
Second Half ends, Dundee 1, Dundee United 4.
Goal! Dundee 1, Dundee United 4. Greg Stewart (Dundee) left footed shot from outside the box to the bottom right corner. Assisted by Craig Wighton.
Corner, Dundee. Conceded by Sean Dillon.
Attempt saved. Luka Tankulic (Dundee) left footed shot from outside the box is saved in the bottom left corner.
Second yellow card to Thomas Konrad (Dundee).
Foul by Thomas Konrad (Dundee).
Gary Mackay-Steven (Dundee United) wins a free kick in the defensive half.
Luka Tankulic (Dundee) wins a free kick in the defensive half.
Foul by Sean Dillon (Dundee United).
Attempt saved. Scott Smith (Dundee United) right footed shot from the right side of the box is saved in the centre of the goal.
Foul by James McPake (Dundee).
Ryan Dow (Dundee United) wins a free kick in the defensive half.
Substitution, Dundee United. Scott Smith replaces Paul Paton.
Attempt missed. Blair Spittal (Dundee United) right footed shot from outside the box misses to the left.
Corner, Dundee. Conceded by Stuart Armstrong.
Goal! Dundee 0, Dundee United 4. Keith Watson (Dundee United) header from the right side of the six yard box to the bottom left corner. Assisted by Paul Paton following a set piece situation.
Foul by Paul McGowan (Dundee).
Stuart Armstrong (Dundee United) wins a free kick on the left wing.
Attempt saved. Blair Spittal (Dundee United) right footed shot from outside the box is saved in the centre of the goal.