Keith Fahey grabbed the only goal of the game to see off midlands neighbours Coventry and hand Birmingham boss Chris Hughton his first points in charge of the npower Championship club.
Hughton, making his competitive bow at St Andrew's, can be credited with the inspired introduction of substitute Adam Rooney which led to the vital breakthrough in an evenly-fought clash.
The summer signing stepped off the bench in the 68th minute and wasted little time making a difference, heading against a post before reacting quickest to tee up the rebound for Fahey to smash home from 10 yards.
The winner came after both sides had wasted a golden opportunity apiece to seize the initiative, Lukas Jutkiewicz and Chris Wood firing off-target when they really should have done better.
Victory gets Birmingham off the mark in what will be a tough quest for an immediate return to the Barclays Premier League, although concern will be growing just 22 miles down the road for a Coventry side who were more than a match for their local rivals but have now lost their opening three matches of the season in all competitions.
Rooney's relegation to the bench in favour of on-loan West Brom striker Wood was Blues' only switch from last weekend's 2-1 defeat at Derby, while skipper Sammy Clingan's return from international duty was Coventry's only change to the side who lost 3-1 at Bury in the Carling Cup in midweek.
Striker Marlon King, who angered Sky Blues fans by controversially switching to Birmingham over the summer, missed out with his troublesome knee problems, while Birmingham's prized centre-back Scott Dann found himself on the bench against his former employers for a second successive weekend.