Summer signings Liam Ridgewell and Garry O'Connor struck for their first Birmingham goals as the Premier League side defeated Sheffield Wednesday in the pre-season friendly at Hillsborough.
Defender Ridgewell, signed for £2million from city rivals Aston Villa yesterday, scored two minutes into his debut, while substitute O'Connor added a second midway through the second half.
Chris Brunt missed a penalty two minutes before the interval as Birmingham edged an even contest.
Owls boss Brian Laws and counterpart Steve Bruce named full-strength sides.
Ridgewell and Franck Queudrue were thrust straight into the starting line-up after completing moves, while three further summer recruits - Daniel de Ridder, Olivier Kapo and O'Connor - were named on the bench as Bruce prepared for Blues' Premier League return against Chelsea next Sunday.
Mikael Forssell, who went off after half an hour with a head injury to be replaced by O'Connor, had a shot blocked before Ridgwell's opener.
Gary McSheffrey's inswinging free-kick found the defender whose headed flick-on bounced beyond Lee Grant.
Jermaine Johnson and Steve Watson each failed to test Colin Doyle before Leon Clarke headed over with the goal beckoning.
Johnson's pace continued to expose Blues' defensive frailties and he won a penalty when fouled by Queudrue two minutes before the interval. Doyle dived to his right to save Brunt's poor spot kick.
A well-worked free-kick involving Glenn Whelan, Brunt and Lee Bullen saw the Owls skipper chip on to the bar 11 minutes into the second half.
But Blues doubled their lead when O'Connor ghosted through to strike low past Grant after 65 minutes.
De Ridder twice went close before Mehdi Nafti's 25-yard effort was palmed away by Grant at full stretch.
Kapo danced through the Owls defence but his shot was poorly directed and Rowan Vine hit the side-netting, while Wade Small tested Doyle at the other end.