Gary Taylor-Fletcher grabbed the only goal as Blackpool secured a shock victory at high-flying Birmingham.
Taylor-Fletcher drilled the winner past Maik Taylor after being teed up by Keith Southern on 47 minutes.
Blackpool's victory margin could have been greater against an out-of-sorts Blues but Taylor made super saves to deny David Vaughan and Ben Burgess.
The home side barely threatened with Cameron Jerome and Kevin Phillips missing half-chances.
Birmingham boss Alex McLeish: "The players know how I feel and they should be feeling terrible as well.
"We never gave the supporters what they wanted and we deserved the criticism from them. If I was a supporter I would have booed as well. It just was not good enough but the Championship is not won or lost in September.
"I expect a positive response from them. That is one thing I have always had from this group of players. It was a poor performance and I was surprised by it.
"But it wasn't a great start, the tempo was slow and we didn't turn the fans on. "As the game wore on Blackpool grew in confidence as we ran out of ideas. There was no guile or craft. I don't think we put more then three passes together."
Blackpool manager Simon Grayson: "I am sure that no-one expected us to come here and win. But overall I thought that we deserved to win.
"We knew we had to be hard to beat and we looked liked we had good shape and good organisation. We kept the ball well and created a few good chances.
"As the game went on we tried to hit them on the counter and we could have scored a couple more.
"Full credit to my defence for the way that they battled and put their bodies on the line. They made blocks and I don't think my goalkeeper had too many saves to make."
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