DJ Campbell claimed his second goal in as many games in the 2-0 victory for 10-man Blackpool as his former club Birmingham blew the chance to climb into second spot in the Coca-Cola Championship.
Victory would have lifted Alex McLeish's side above Reading and into the automatic promotion places, but first-half strikes from Campbell and midfielder Keith Southern sealed their fate.
Not even the 74th-minute dismissal of substitute Claus Jorgensen - following an off-the-ball challenge on Lee Bowyer that left the former Leeds midfielder needing treatment - could take the gloss off Blackpool's success.
Blackpool deserved their first win since Tony Parkes and Steve Thompson were placed in caretaker charge in late December on the strength of their first-half superiority.
Birmingham created next to nothing throughout as their winless run in all competitions extended to four games to leave McLeish with much food for thought as he bids to bounce back from last season's relegation.
His men were second best to everything in the first half and nobody impressed more for Blackpool than Campbell.
The diminutive striker, who spent 18 months at St Andrew's between January 2006 and July 2007, is on loan at Blackpool from League One leaders Leicester until the end of the season.
Having scored on his debut for the Seasiders in last weekend's 2-1 defeat at Coventry, Campbell was on the mark again for his new club with a 13th-minute header.
Gary Taylor-Fletcher swung in a teasing cross from the left flank and Campbell, 27, met the ball with a firm header from six yards.
After 37 minutes, it was 2-0 as Southern was afforded the time and space to collect possession and strike a fierce right-foot shot from 25 yards past Maik Taylor.
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