Town were a condemned to a 3-1 home defeat by Kyle Bartley's second-half double for Birmingham.
But the on-loan Swansea defender's day was soured when he was sent off after being shown a second yellow card for the celebration of his match-clinching goal.
Town had trailed to Nikola Zigic's early opener, but levelled through Anthony Gerrard before the break.
Boss Mark Robins made two changes in the wake if the 1-0 defeat at Wigan, with Gerrard returning at centre-back in place of Joel Lynch and Sean Scannell coming in for Jonathan Hogg.
While midfielder Hogg was ruled out of the Championship clash with a knee injury, Lynch, recovering from a thumb operation, dropped to the bench.
But he was soon on the pitch as Town lost skipper Peter Clarke after just six minutes after he came off worst in a crunching challenge.
The change seemed to knock Town out of their stride, and Birmingham took advantage with an 11th-minute opener.
Big Serbian striker Zigic was on hand to knock home from close range after ex-Town striker Lee Novak's shot was parried by Alex Smithies.
Town gradually got back into the game, and after Danny Ward's free-kick was well cleared, the equaliser came in the 31st minute.
Adam Hammill claimed another assist as he flighted in a free-kick which Gerrard glanced home for his first goal of the season.
Birmingham's Novak and Town's Scannell both had shots saved as play swung from end to end before the break.
There were chances for both sides in the 55th minute, as Novak had a piledriver saved before Hammill put a low angled shot across the face of goal.
Town made a double substitution after 63 minutes, with Oscar Gobern and Danny Carr coming on for Ollie Norwood and Jon Stead.
But they were trailing again within 60 seconds as Bartley headed home from Jesse Lingard's corner.
Ward shot just wide, but Town were looking a little laboured in theirsearch for a second equaliser.
And their task became even harder when Bartley headed his second goal of the game from a free-kick in the 81st minute.
Already cautioned, the scorer was shown a red card after referee Gavin Ward deemed his celebration a bookable offence.
