Birmingham picked up a point in their relegation fight as leaders Chelsea turned in a below-par performance.
Chelsea struggled in the first half against Birmingham
Emile Heskey missed three reasonable chances for Birmingham in the first half, while Oliver Tebily forced a fine save from Chelsea goalkeeper Petr Cech.
Chelsea finally shook off their torpor with Maik Taylor saving well from Didier Drogba and Hernan Crespo.
In the last minute the Argentine also missed a good opportunity, while Ricardo Carvalho headed badly wide.
Chelsea were out of sorts in the first half, with passes going astray and even the normally impeccable Frank Lampard guilty of some sloppy play.
The Premiership leaders were more effective after the interval and Asier del Horno and Damien Duff both had the ball in the net, only to be adjudged offside.
In that promising opening period for Birmingham, Steve Bruce's side kept a tight rein on wingers Duff and Arjen Robben, thereby isolating Drogba in attack.
If Birmingham managed to unsettle Chelsea, the home side proved less successful in scoring against them.
Heskey has managed just four Premiership goals this season and his lack of confidence was amply demonstrated in the opening 20 minutes as he passed up three good chances.
The Birmingham striker first blazed over following Paulo Ferreira's miscued clearance and headed well wide from a Jermaine Pennant free-kick.
Matthew Sadler's swinging cross then found Heskey, but having worked an angle, the hapless striker shot over the bar to the groans of the Birmingham fans.
It was left to a Birmingham defender to draw Cech into action, Tebily's rising shot impressively tipped over by the Chelsea goalkeeper.
Birmingham keeper Taylor showed equally smart reactions to push away a Robben shot after Drogba had quickly taken a free-kick to surprise the home side's defence.
Early in the second half, Taylor saved well from Drogba's flicked volley when Del Horno crossed from the left.
Drogba's next touch was altogether less assured as he lashed the ball over the bar following a dangerous Robben run.
Lampard was the next Chelsea player to glimpse a sight of goal, but his shot was too high.
With Chelsea in the ascendancy, Bruce introduced Mikael Forssell for the ineffective DJ Campbell, though the former Chelsea striker made little impact.
Chelsea substitute Crespo threatened to win the game for the leaders late on, going close with a close-range volley that Taylor clutched to his chest.
Carvalho also might have done better with a header from a Chelsea corner, but Birmingham held on to secure a point.
Birmingham manager Steve Bruce:
"We were looking for a response after the Liverpool game and for people to do their jobs.
"We've restored a bit of pride, and it has earned us a point in the mini-league we're facing to stay up between ourselves, Pompey and WBA.
"Everyone produced the performance we have been wanting and needing, and I hope it will give everyone a lift."
Chelsea manager Jose Mourinho:
"The result is a fair one. Birmingham fought for 90 minutes. All their players were very committed.
"It would have been very nasty for them to have lost a match into which they put absolutely everything.
"But we scored a clear goal. You can say what you want, and your pundits can discuss it, but Asier Del Horno's goal should have stood."
Birmingham: Maik Taylor, Tebily, Cunningham, Martin Taylor, Sadler, Pennant, Clemence, Butt (Kilkenny 88), Johnson, Heskey, Campbell (Forssell 57).
Subs Not Used: Vaesen, Latka, Lazaridis.
Chelsea: Cech, Paulo Ferreira, Ricardo Carvalho, Terry, Del Horno (Crespo 64), Robben, Lampard, Makelele, Duff (Joe Cole 64), Drogba, Gudjohnsen (Essien 68).
Subs Not Used: Cudicini, Huth.
Ref: D Gallagher (Oxfordshire).