Barclays Premier League leaders Chelsea had to be content with a Boxing Day point at in-form Birmingham.
While Chelsea enjoyed the better chances, it was Birmingham who had the ball in the net at St Andrew's, Christian Benitez poking it over the line and apparently being played onside by an injured Didier Drogba only to see the flag raised against him.
The visitors, defending a four-point lead over second-placed Manchester United, had excellent chances to win it themselves as Branislav Ivanovic, Daniel Sturridge, Alex and Florent Malouda all went close. Malouda, meanwhile, was dismissed in the closing stages after receiving a second caution.
Chelsea boss Carlo Ancelotti handed Sturridge - whose father Michael and uncle Simon are former Birmingham players - his first Barclays Premier League start in the absence of the injured Nicolas Anelka.
Birmingham were unchanged for the seventh successive game as they attempted to build on a nine-match unbeaten run.
The home side carved out the first chance less than a minute into the match, Barry Ferguson catching Chelsea cold with a sweeping pass that Cameron Jerome brought under control only to fire off target.
Chelsea right-back Ivanovic came close to opening the scoring in the 11th minute when he rose to meet Malouda's corner but headed just over.
Frank Lampard scooped a 35-yard effort well over as Chelsea continued to push forward, while Juliano Belletti headed just wide from a tight angle in the 18th minute.
Didier Drogba continued the assault when he met Ivanovic's cross from deep with a powerful volley that whistled wide, and soon afterwards Sturridge blasted a shot that Joe Hart did well to save.
Lampard's snap-shot forced another good save from Hart after good forward play by Drogba to create the opening.
Birmingham had the ball in the net in the 31st minute only for it to be ruled out somewhat harshly.
When the ball was fired back into the box after a free-kick, with Drogba lying injured, Liam Ridgewell directed the ball towards goal - only for Benitez, apparently in an offside position, to stab it over the line and see the goal ruled out by the assistant referee's flag. However, television replays suggested the home fans' frustration was justified, with Drogba playing the striker onside.
Chelsea hit back, with Alex's powerful free-kick from distance smashing into the crossbar with half-time approaching.
In added time, Sturridge had a glorious opportunity when Drogba crossed from the right but the youngster's volley at the far post was narrowly wide.
After a quiet opening to the second half in which Chelsea probed without making headway, City striker Benitez cut inside for a shot that Terry blocked well with his head in the 58th minute.
Livewire Benitez was Birmingham's dangerman and he forced Malouda to foul him and concede a yellow card on the hour following more determined dribbling.
From the resulting free-kick, Sebastian Larsson curled a trademark effort towards the top left-hand corner that Petr Cech did well to save, injuring himself against the post in the process but recovering quickly.
The visitors continued to press at the other end and Belletti and Lampard had half-chances, while Ancelotti replaced Sturridge with Salomon Kalou in the 67th minute.
Kalou nearly had an immediate impact as his cross from the right found Malouda, who miscued woefully in lots of space.
Hart produced another excellent save from Drogba's shot in the 71st minute before Lampard scuffed a first-time effort from the corner that followed.
Birmingham broke forward in the 74th minute after James McFadden fed Jerome but the striker could not provide an end product as he was smothered in the Chelsea box.
Malouda's nightmarish afternoon was complete when he received a second yellow card in the closing stages for an ill-judged challenge on Stephen Carr, while substitutes Keith Fahey and Damien Johnson both created half-chances for Birmingham during six minutes of added time.