Match ends, Middlesbrough 3, Birmingham City 1.
Birmingham lie only four points above the Championship relegation zone after defeat at nine-man Middlesbrough.
Danny Graham slotted home for the hosts before Jacob Butterfield doubled the lead from distance.
Emyr Huws's dipping shot from 35 yards got one back for Blues, before Boro pair Kenneth Omeruo and Ben Gibson were both sent off for second bookings.
But Lee Tomlin smashed home his first goal for Boro to seal the points.
A third successive win leaves the Teessiders eight points off the play-off places but, with only five games remaining, a top-six finish looks unlikely.
The deadlock was broken just before the half-hour mark when Grant Leadbitter's corner from the right was nodded down to Graham, who converted from inside the six-yard box
Less than two minutes later, a long-range strike from Butterfield flew past Birmingham goalkeeper Darren Randolph to double Boro's advantage.
The Blues refused to lie down, though, and, after Manchester City loanee Huws had halved the deficit with a thunderbolt, Shinnie came close to equalising before the break from Callum Reilly's cross.
Randolph twice denied Graham after the restart as Aitor Karanka's side threatened to put the match to bed while, at the other end, Ibe - who came on as a second-half substitute for Shinnie - fired off target with a low drive.
Omeruo and Gibson were both shown second yellows for fouling Ibe and Nikola Zigic respectively.
But, despite Birmingham's two-man advantage, Tomlin capitalised on a defensive mix-up between Tom Thorpe and Paul Robinson to smash the ball into the back of the net.
Middlesbrough manager Aitor Karanka: "I don't want to speak about the play-offs because the moment we speak about the play-offs, we will lose our next game.
"I prefer to think about the next game at Burnley as being one against a team near the top of the table and we have to go there to win the game.
"We have won the last three games and for this I am very happy."
Birmingham manager Lee Clark: "Our decision-making in the second half was astounding.
"It's starting to scare us, to be honest, in terms of the young players coming through.
"They need the mentality of how to win games. I think they'd rather do a trick or a flick rather than put the ball in the net."
- 3FriendSubstituted forWoodgateat 20'minutes
- 25OmeruoBooked at 80mins
- 22GibsonBooked at 86mins
- 6ButterfieldSubstituted forTomlinat 77'minutesBooked at 89mins
- 14WilliamsSubstituted forLedesmaat 67'minutes
- 23SpectorSubstituted forAdeyemiat 83'minutes
- 17ReillyBooked at 56mins
- 4RobinsonBooked at 64mins
- 22ShinnieSubstituted forIbeat 66'minutes
- 12NovakSubstituted forZigicat 45+5'minutes
- Carl Boyeson
- Shots on Target
Second Half ends, Middlesbrough 3, Birmingham City 1.
Attempt missed. Nikola Zigic (Birmingham City) header from the centre of the box is too high. Assisted by Chris Burke with a cross.
Foul by Lee Tomlin (Middlesbrough).
Paul Caddis (Birmingham City) wins a free kick in the defensive half.
Attempt saved. Jordon Ibe (Birmingham City) right footed shot from the left side of the box is saved in the bottom left corner.
Attempt missed. Callum Reilly (Birmingham City) left footed shot from the right side of the box is high and wide to the left. Assisted by Chris Burke following a corner.
Corner, Birmingham City. Conceded by Grant Leadbitter.
Attempt blocked. Jordon Ibe (Birmingham City) right footed shot from outside the box is blocked. Assisted by Emyr Huws.
Foul by Lee Tomlin (Middlesbrough).
Emyr Huws (Birmingham City) wins a free kick in the defensive half.
Attempt blocked. Emmanuel Jorge Ledesma (Middlesbrough) left footed shot from the left side of the box is blocked.
Lee Tomlin (Middlesbrough) is shown the yellow card for excessive celebration.
Goal! Middlesbrough 3, Birmingham City 1. Lee Tomlin (Middlesbrough) right footed shot from the centre of the box to the bottom left corner.
Second yellow card to Ben Gibson (Middlesbrough) for a bad foul.
Foul by Ben Gibson (Middlesbrough).
Chris Burke (Birmingham City) wins a free kick in the attacking half.
Attempt saved. Jordon Ibe (Birmingham City) left footed shot from the left side of the box is saved in the centre of the goal.
Offside, Birmingham City. Paul Robinson tries a through ball, but Jordon Ibe is caught offside.
Substitution, Birmingham City. Tom Adeyemi replaces Jonathan Spector.