Blues will require a second game at St Andrews to overcome Chris Hughton's well-drilled side as Andre Villas-Boas sees his job become more insecure following more disappointment
David Murphy gave the Championship side the lead, firing home after indecisive defending, Mata's spot-kick miss didn't help Chelsea's cause but the Blues fought back and equalised through Daniel Sturridge's header.
Both teams made several changes for the tie, Chelsea made four alterations to the side that were beaten by Everton last weekend, Ryan Bertrand, Gary Cahill, John Obi Mikel and Ramires coming in, but captain John Terry was left out all together as his knee problems continue.
Chris Hughton made five changes after seeing his side draw 0-0 with Hull City in midweek, former Spain international Pablo Ibanez replaced Gary Caldwell in the heart of defence and exciting young winger Nathan Redmond was handed a start in place of Chris Burke.
The game started sluggishly as Chelsea struggled to penetrate Birmingham's five-man midfield. The Championship side were also dealt an early blow as captain Stephen Carr was forced off after just 12 minutes with injury, Jonathan Spector replacing him.
And the Premier League side were punished after 20 minutes as Keith Fahey's corner from the left was flicked on and as Chelsea's defence dithered, the ball found Murphy unmarked at the far post who slammed the ball home from six yards to stun the majority of Stamford Bridge.
Incredibly Chelsea were given a golden chance to get back into the game just moments later, Ramires carried the ball into the penalty area and surged past Wade Elliott who could only bring the Brazillian down, Martin Atkinson duly pointing to the spot.
Juan Mata stepped up confidently but saw his effort tipped on to the post by Doyle, sprawling down to his right as the away end erupted for a second time.
Andre Villas-Boas' side looked to dominate in their search for an equaliser, David Luiz set off on a skilful run and was illegally halted by Jordon Mutch who was booked, the former Benfica defender picked himself up and hitting a dipping free-kick from 30 yards that needed tipping over by Doyle.
The home side continued to put pressure on their opponents, Sturridge latched onto a Fernando Torres knock-down and fired over before Mikel dispatched a long-range volley just wide.
A tame Mata header was the last of Chelsea’s first half chances and they went in for the break behind as much of Stamford Bridge made their displeasure known.
Villas-Boas changed his side for the second period, introducing Didier Drogba in place of Torres who had once again looked to be lacking the confidence or ability to bring his goal-drought to an end.
The Ivorian's introduction seemed to lift the home crowd and he looked to get into the thick of the action immediately, just failing to latch on to a Raul Meireles chipped pass.
After 10 largely eventless second-half minutes, Villas-Boas made another attacking swap, replacing Mikel with Salomon Kalou.
Mata fired an effort wide before Chelsea finally levelled the scores, Ivanovic was given too much time to pick a cross from the right and Sturridge was left to meet the ball with a firm header that nestled in the corner of the net.
The Blues were now playing with improved confidence and beginning to dominate with Mata again at the heart of things, firing a dangrous ball across Birmingham's six-yard line before Meireles hit a deflected effort just over following a corner from the diminutive Spaniard.
Jordon Mutch hit a long-range free-kick that Cech saved comfortably in a rare foray forward for the Bluenoses before Chelsea made their final change, Frank Lampard sent on to find a late equaliser in place of Mata.
Ivanovic tumbled in the Birmingham area but no penalty was awarded before Redmond spurned a good chance at Cech's goal, choosing to shoot with his right-foot despite an unfavourable angle.
Lampard hit a free-kick into the wall but Chelsea were unable to find a winner and will now go into their Champions League tie at Napoli in mid-week under severe pressure after another disappointing result.
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