It brought the tantalising prospect of Champions League football at the City of Manchester for the first time a sizeable step closer after their latest success.
A rather nondescript opening half exploded to life with four goals in a dramatic five-minute spell shortly before the break as City took control.
There was an element of good fortune about the penalty which resulted in Carlos Tevez opening the scoring with his 27th goal of the season.
There appeared to be minimal contact when Emmanuel Adebayor went down in the box following a challenge by Scott Dann.
There was no disputing the second goal two minutes later when Nedum Onuoha found the net for the first time this season with a far-post diving header from Adam Johnson's corner, although the ball appeared to take a slight deflection off Tevez's foot.
Birmingham almost immediately halved the deficit when Cameron Jerome, who looked suspiciously offside, was left unmarked at the far post to head home a James McFadden cross.
City quickly restored their two-goal advantage when Craig Bellamy opened the Birmingham defence on the left and his low cross was slotted home by Adebayor from inside the six-yard box.
The two-goal cushion looked anything but secure as Birmingham made a spirited start to the second half as Jerome beat keeper Shay Given to a cross but headed narrowly wide, while the City keeper also made a super save with his legs to deny McFadden.
City needed a fourth goal and that so nearly came midway through the second period when Birmingham keeper Maik Taylor pulled off a fantastic fingertip stop to keep out a free-kick from Tevez which was destined for the top corner.
The goal which finally killed off Birmingham came in the 74th minute when right-back Onuoha played a one-two with Tevez and burst through the visiting defence to score with a well-placed shot.
After failing to find the net all season, suddenly Onouha had two goals in little over half an hour.
City even added a fifth in the 88th minute when Adebayor latched onto a clearance from Given and raced clear to slot home a low shot for his 13th goal of the campaign.