Birmingham made the most of a dominant first-half performance and an awful error by keeper Thomas Sorensen to secure victory against Aston Villa.
Clinton Morrison struck after just nine minutes when his speculative effort slipped through Sorensen's fingers.
Birmingham doubled their lead when David Dunn converted Damien Johnson's cross to finish a smart counter-attack.
The visitors missed further chances and Villa improved after the break but Gareth Barry's goal was a consolation.
David O'Leary's side had earlier got the ball into the net, but it was via the hand of Barry, who was subsequently booked for the misdemeanour.
The decision was the right one, but a goal may have been fair reward for intense pressure from Villa, who looked a different team in the second half.
However, their poor display, and Birmingham's excellent work, in the opening 45 minutes should have left the result beyond doubt.
Birmingham strikers Morrison and Emile Heskey were rampant from the first whistle and the pair combined superbly to strike the first blow.
Heskey's strength allowed him to nod the ball onwards, and Morrison held off Mark Delaney to get his shot away.
It should have been comfortably gathered by Sorensen, but this derby has a habit of embarrassing Villa keepers and the series continued.
Sorensen's fumble will be no doubt be added to Peter Enckleman's blunder in a goalkeeping video nasty.
But he could do nothing about Birmingham's second - the fault there lay with defender Jlloyd Samuel, who allowed Johnson to sprint past him before delivering a telling cut-back.
Dunn's arrival in the box was perfectly timed and his shot equally well struck.
Villa were second-best all over the pitch, with Robbie Savage snapping in trademark style and Matthew Upson authoritative in defence.
Heskey was proving a real menace up front and he was unlucky not to further his side's lead when his shot hit the post after he jinked past Olof Mellberg.
The Villa defender's frustration was obvious when he became involved in a mass brawl between players, sparked after Johnson's challenge on Barry.
Mellberg and Johnson went into the book as tempers flared.
Later, in the second half, the impressive Dunn was taken off by Steve Bruce to prevent his player picking up a second caution as the game continued to have an edge.
Villa pressed forward and almost scored just after the restart when Carlton Cole volleyed Nolberto Solano's cross.
Maik Taylor proved equal to the shot, despite it being the first time he had been called into making a save.
Clear cut chances remained few for Villa, despite their greater share of possession.
Solano, who was much-improved after a quiet opening, twice delivered crosses into the box but there were no Villa players supporting.
However, when Juan Pablo Angel did make it into the penalty area he was unlucky not to win a penalty as Olivier Tebily appeared to handle his shot.
Two minutes into injury time, Villa finally made the breakthrough as Barry collected a long pass and cut inside Tebily.
But his smart finish came too late for his side, whose dismal record of never beating Birmingham in the Premiership remains.