Clayton Donaldson’s 41st minute penalty has given Birmingham a 1-0 half-time lead over the Blues at St Andrew’s.
Myles Kenlock came in for the injured Jonas Knudsen at left-back in an otherwise unchanged Town side. The Dane travelled but missed out with an unspecified knock.
Andre Dozzell replaced Teddy Bishop, who is out for up to a month with an ankle ligament injury, on the bench.
The Blues, wearing their all white away kit, were first to threaten in the third minute when Adam Webster sent Luke Varney away on the right. Saturday’s goalscorer crossed towards David McGoldrick, who failed to make contact as he looked to volley. Birmingham keeper Tomasz Kuszczak eventually cleared the danger ahead of the lurking Jonathan Douglas.
Blues keeper Bartosz Bialkowski was called into action for the first time on 10 when Jonathan Grounds’s long throw from the left bounced awkwardly in the area. However, the Pole punched away.
Town had looked the more dangerous side in the early stages, however, and in the 12th minute Tom Lawrence crossed from the left and McGoldrick hit a shot on the half-turn, which deflected over off Michael Morrison.
Following the corner, the ball was cleared out to Kenlock, who had made a confident start, but his shot struck McGoldrick.
After Bialkowski had rushed off his line to clear the ball ahead of Maikel Kieftenbeld, Lawrence made a pacy run down the left and won a corner. The on-loan Leicester man took the flag-kick and Christophe Berra nodded down at the far post but no Town player was on hand to profit from it.
As the game reached the 20-minute mark Jonathan Spector sent a dangerous low ball across the Town area from the right but no one was able to get a touch.
A minute later, Webster found Kenlock on the right with a classy cross-field ball. The 20-year-old left-back crossed but Douglas’s header looped wide.
Bialkowski was forced to save on 25 when Berra headed away from Donaldson but only succeeded in finding Lukas Jutkiewicz 20 yards out, from where the striker hit a shot which the Town keeper palmed away to his right.
Kuszczak made an even better save at the other end on 32 after Lawrence had made another dangerous run down the left. The Welsh international cut the ball across and Morrison stabbed the ball out to McGoldrick, who hit a first-time effort which the former Manchester United man did well to push over.
The Blues had had the better of the half but so far without having anything to show for it. But on 36 there was danger at the other end when Spector crossed from the right towards David Davis but the midfielder was only able to head into the stand from a tight angle.
David Cotterill picked up the game’s first booking on 38 for a foul on Ward, then a minute later Blues skipper Luke Chambers joined him in the book for pulling back Jutkiewicz on halfway.
Birmingham were beginning to look the more threatening side and on 40 Jutkiewicz hit a shot which deflected wide off Chambers after a corner had been cleared and looped back into the box.
From the resultant flag-kick, the home side were awarded the penalty from which they would take the lead.
Jutkiewicz hit another shot and Varney tried to block but only succeeded in stopping it with his arm and referee Darren Bond pointed to the spot.
The Town players protested in vain, and with little cause, before Donaldson stepped up and chipped down the middle as Bialkowski dived to his left.
As the game moved into injury time goalscorer Donaldson was stretchered off after a long spell of treatment having fallen awkwardly when challenging with Webster on halfway. Che Adams took over in the home side’s attack.
Birmingham’s half-time lead was harsh on the Blues who had had the better opportunities up to the penalty with Kuszczak having made the game’s most significant save from McGoldrick.
However, the home side had started to look more dangerous just prior to winning the penalty with Jutkiewicz having hit a number of strikes from the edge of the box.
Birmingham: Kuszczak, Spector, Morrison, Shotton, Grounds, Cotterill, Gleeson, Kieftenbeld, Davis, Donaldson (Adams 45), Jutkiewicz. Subs: Legzdins, Robinson, Tesche, Solomon-Otabor, Maghoma, Dacres-Cogley.
Town: Bialkowski, Chambers (c), Webster, Berra, Kenlock, Skuse, Douglas, Ward, Lawrence, McGoldrick, Varney. Subs: Gerken, Emmanuel, Bru, Dozzell, Williams, Sears, Pitman. Referee: Darren Bond (Lancashire).