A Sebastian Larsson goal ten minutes into the second half enabled them to clinch the win which took them back to the top of the Championship.
It was only Larsson's second league goal of the season and it could not have come at a more important time as Birmingham had to grind out their win.
In the process they gained revenge for their defeat early in the season at Ninian Park, but it was far from conclusive.
On the basis of this match Birmingham's investment of £130,000 in relaying their pitch could easily prove very costly and cost them promotion. It was a quagmire of a pitch which completely ruined the game and prevented both teams from playing any football.
Cardiff's aggressive style appeared better suited to the conditions and the Welshmen battled hard and at least deserved a point for their efforts.
Birmingham were often put out by the gritty determination of the Cardiff side. There are no frills about the Bluebirds and they raised their game on the back of some hard work.
The industry of skipper Riccardo Scimeca was particularly noticeable but it was the nippy play of Michael Chopra which caused Birmingham all sorts of trouble.
He popped up in all sorts of places and caused Birmingham considerable confusion at the back, where Bruno N'Gotty in particular was exposed.
In a concentrated spell of attacking play Scimeca saw his close-range header well saved by Birmingham's up and coming goalkeeper, Colin Doyle.
Immediately afterwards the young Irishman had to dive at the feet of Chopra. The striker appealed for a penalty as Doyle received extended treatment for a head injury.
In heavy rain, on a bog-like pitch, Birmingham struggled to come to terms with the opposition when their approach was often too slow and predictable.
Neither Nicklas Bendtner nor Rowan Vine could make any impact, while teenager Fabrice Muamba struggled in midfield when he was often let down by his poor passing.
Birmingham had another let-off midway through the first period when Chopra again outpaced a sluggish defence, only for Steven Thompson to miss the low cross from the right.
Thompson produced another close-range header which Doyle safely clutched low down.
But conditions continued to deteriorate badly and Cardiff continued to appear the more dangerous, but in the 55th minute Birmingham, to the relief of their fans, broke the stalemate.
A left-wing cross slithered off Bendtner to Larsson lurking on the right and the former Arsenal winger rammed home the vital opening goal for only his second league strike of the season.
Only the brilliance of Doyle, who has grabbed his first-team chance with both hands, kept Birmingham ahead.
Roger Johnson hammered in a powerful dipping shot which Doyle finger-tipped over the bar to enhance his growing reputation.
Cardiff's keeper, Neil Alexander, also covered himself with glory in the final ten minutes pushing away on-target efforts from Gary McSheffrey and Stephen Clemence.
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