Clinton Morrison supplied the ammunition as Emile Heskey and Darren Carter fired Birmingham past Leeds.
Julian Gray's drive tested United keeper Neil Sullivan before Morrison released Heskey who clipped his shot over Sullivan and in off the far post.
Carter converted Morrison's first-time cross for 2-0 before sliding his second home from another Morrison centre.
Blues keeper Maik Taylor then denied Frazer Richardson, Matthew Kilgallon, Aaron Lennon and David Healy.
United were over-run in the early stages, but deserve credit for not going down without a fight.
Heskey's well-taken early goal from Morrison's simple pass was deserved and although the visitors lost Nathan Blake and Michael Duberry through injury, they regularly tested Blues keeper Taylor.
Richardson's well-struck shot was well gathered at the foot of a post, while Kilgallon directed a header straight at Taylor.
But the Blues were more clinical in front of goal with Carter twice benefiting from Morrison's build-up play on the right.
Simon Walton glanced a header wide for United, while Taylor did well to push Lennon's downward volley over the bar and then denied Leeds a consolation by holding on to Healy's low shot.
Birmingham boss Steve Bruce:
"Darren Carter's contribution was excellent and he has done exceptionally well since coming back from Sunderland.
"We saw during the match everything that the modern midfield player needs - strength, power, runs forward and composure in the penalty box.
"Darren deserves a massive pat on the back and going to Sunderland has definitely helped him."
Leeds boss Kevin Blackwell:
"I was proud of the side. The difference between the teams was Premiership quality where it matters most and that was in the penalty area.
"But last season we came here and got absolutely battered and you couldn't say that was the case here.
"If we had taken our chances it might have been closer."
Birmingham: Maik Taylor, Melchiot, Cunningham, Upson,Lazaridis (Clapham 40), Anderton (Tebily 77), Clemence, Carter,Gray, Heskey (Blake 67), Morrison.Subs Not Used: Vaesen, Yorke.
Booked: Upson.
Goals: Heskey 11, Carter 21, 65.
Leeds: Sullivan, Kelly, Kilgallon, Duberry (Pugh 22),Richardson, Lennon, Wright, Gregan, Walton, Healy,Blake (Joachim 19).Subs Not Used: Carson, Ricketts, Griffit.
Att: 25,159
Ref: G Poll (Hertfordshire).