Keith Southern's strike before half-time sealed Blackpool's victory
Birmingham's promotion bid suffered a setback as 10-man Blackpool ran out winners at Bloomfield Road.
On-loan striker DJ Campbell, playing against his former club, claimed his second goal in two games for Blackpool, heading in Joe Martin's teasing cross.
Keith Southern doubled his side's lead before half-time, rifling a shot passed goalkeeper Maik Taylor from 25 yards.
Blackpool midfielder Claus Jorgenson was sent off late on for an off-ball-challenge with Lee Bowyer.
Blackpool caretaker boss Tony Parkes: "You need victories if you want to get the job and this was a big victory against one of the top sides in the division.
"It was well deserved because they didn't have too many chances and when we went down to 10 men we battled hard and hung on for the result."
Birmingham manager Alex McLeish: "It's a lost opportunity but there are a lot of games left and I don't think it's time to press the panic button.
"We're disappointed but we've got to show perseverance and some of the players must realise that they've got to give us a lot more than they've given us in this game.
"There are no excuses and, as a team with our aspirations, the players know they have to do much better than that."
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