Franck Queudrue's 87th-minute header secured Birmingham three huge points with a 1-0 win over against Bristol City and moved the midlands club back into the automatic promotion places in the Coca-Cola Championship.
A much-improved Blues side dominated their fellow promotion hopefuls for large spells of the encounter and eventually got the win they deserved as Queudrue powerfully head home Lee Bowyer's corner to send the home crowd into raptures.
In the night's other game Sheffield United set a new club record of 12 away league games unbeaten with a 2-1 victory over Coventry at the Ricoh Arena.
At St. Andrews Birmingham looked set to rue a series of wasted opportunities as centre-backs Radhi Jaidi and Martin Taylor both hit the crossbar, while Bowyer headed wide from close range and saw goalkeeper Adriano Basso produce a superb stop to deny him.
The win was nothing less than the hosts deserved, but it could have been so different had former Blues striker Dele Adebola not wasted a great chance after only two minutes, dragging his shot across goal and wide after being sent clear.
The victory, coupled with Birmingham's win at Ashton Gate earlier in the season, meant Blues became the first side to record a league double over Bristol City since their promotion to the Championship in 2007.
Across the midlands Kevin Blackwell's side secured three points which kept their play-off challenge firmly on track and moved them up to fourth in the table - six points away from an automatic promotion spot.
The Blades took the lead in controversial circumstances in first-half injury-time through Leigh Bromby. Television replays showed that the defender's effort did not cross the line.
But there was no argument in the 54th minute when captain Chris Morgan powered home a header to double his side's advantage.
City skipper Scott Dann replied with a headed goal midway through the second half to set up a tense finale but United held on.
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