Aston Villa self-destructed as jubilant Birmingham romped home in the local derby as Clinton Morrison, a Peter Enckelman own goal and Geoff Horsfield secured victory.
Morrison opened the scoring after half an hour with his third goal in two games to set City on their way. Second half substitute Darius Vassell put a header after Nico Vaesen had stranded himself flapping at the ball and moments later Gareth Barry was inches away with a low curled free-kick.
Villa's strenuous efforts then collapsed in farcical circumstance as a bizarre own goal from Enckelman handed Birmingham some breathing space.
The keeper's lazy attempt to control Mellberg's throw-in saw the ball take a touch off his boot and roll across the goal-line.
Birmingham could not believe their luck and nor for that matter could Villa. Enckelman's expression said it all, his feelings not eased by the jubilant taunting of a fan who gestured in his face after running onto the pitch.
Substitute Geoff Horsfield rounded off an agonising night for Villa with a clean finish, after Alpay had failed to control a through ball.