Substitute Cameron Jerome scored a late winner at Watford to keep Birmingham's promotion bid on track.
Substitute seals crucial victory for promotion chasers
Birmingham took a massive step in their bid to return to the top flight thanks to a late winner from substitute Cameron Jerome at Watford on Saturday.
The 1-0 victory at Vicarage Road means Alex McLeish's side are now four points above third placed Sheffield United, who have a game in hand and take on play-off chasing Burnley at Turf Moor on Monday.
Jerome had been on the pitch for just three minutes when he smashed a shot into the top corner with 17 minutes to go to seal the crucial win.
Watford goalkeeper Scott Loach had earlier had an inspired 45 minutes to frustrate a dominant Birmingham in the first half.
But Brendan Rodgers' side were much improved after the break and could have gone ahead themselves before Jerome made the breakthrough.
Loach, who was handed a new contract this week, kept out Damien Johnson, O'Connor, James McFadden and Lee Bowyer with good saves in the opening period as Birmingham entirely controlled the game.
The vastly experienced duo of Johnson and Bowyer ran Watford's young midfield ragged as the Blues created chances at will but were unable to find a finish as the hosts struggled to get out of their own half.
Full-back Lloyd Doyley did flash a speculative 25-yarder marginally wide on a rare breakaway but the visitors continued to monopolise possession as McLeish grew more and more frustrated on the touchline.
Seb Larsson then had perhaps the clearest sight of goal in the 39th minute. The Swede cushioned a header into Bowyer on the edge of the area before running on to a perfectly weighted return ball and smashing in a volley that Loach kept out at his near post.
The Watford goalkeeper then produced his best save of the half to dive full length and tip Bowyer's rasping drive from 20 yards up and away.
Rodgers brought striker Grzegorz Rasiak on at the break in a bid to offer some attacking threat and the Pole almost created the opener instantly.
A quick throw found Rasiak in space on the right flank and he drilled in a powerful cross which the arriving Danny Rose flung himself at but the youngster could not keep his shot on target.
Tommy Smith then ran into the area and cut his cross back just behind Rasiak as the Hornets started the second period well.
Rasiak then forced Colin Doyle into his first serious save of the afternoon when he planted a header into the bottom corner from a Jobi McAnuff cross but the Northern Ireland international used his 6ft 5ins well to get down and tip the ball wide.
Kevin Phillips and Jerome were both introduced by McLeish and it was former Cardiff striker Jerome who finally broke the deadlock with 17 minutes left.
Johnson fed Jerome down the left channel and his pace took him clear of Jay DeMerit.
However he looked to have been forced wide and after cutting in from the left looked set to lay the ball off.
But the forward instead managed to turn onto his right foot and hammer a shot which looped up off the toe of Watford midfielder Ross Jenkins and flew past Loach into the top corner.
Watford forced a few moments of panic as the piled bodies forward but Birmingham held on for a huge win.