Birmingham put a dent in Middlesbrough's bid for promotion to the Premier League as the hosts came from behind to win 3-2 at St Andrews on Friday.
Middlesbrough would have moved level on points with Championship leaders Cardiff if they had beaten the Blues, but Tony Mowbray's side twice squandered the lead and remain in third spot after Marlon King's late winner for Birmingham.
The visitors had gone ahead in the 14th minute when captain Grant Leadbitter headed in an Andy Halliday cross.
But King levelled with a penalty on the stroke of half-time after being tripped by Middlesbrough defender Andre Bikey.
In-form Australian striker Scott McDonald restored Middlesbrough's lead when he punished sloppy defending from Pablo Ibanez to fire home after a goalmouth scramble in the 62nd minute.
However, Birmingham, who have struggled for much of the season, hit back through Wade Elliott, who equalised in the 66th minute with lob that should have been saved by Jason Steele.
And King bagged the winner with nine minutes remaining when the former Watford forward converted a pass from Peter Lovenkrands.
The defeat leaves Middlesbrough two points behind second placed Crystal Palace, while Birmingham's second win in seven attempts at home will slightly ease the pressure on under-fire boss Lee Clark, whose side are now nine points clear of the relegation zone.