They more than deserved their vital point in the battle for Premiership survival against the Premiership leaders, who have suddenly lost their flair away from Stamford Bridge.
Birmingham have never beaten Chelsea in the Premiership and their last success over the Londoners at St. Andrew's was 20 years ago but they came close to changing this statistic.
They did survive an anxious last few minutes when Hernan Crespo shot straight at goalkeeper, Maik Taylor, and Claude Makelele headed over the bar.
The admiration of Birmingham manager Steve Bruce for the all-conquering Chelsea side is fully justified, but he was extremely proud of his own team as they battled back after recent setbacks.
On this occasion the egg-shell thickness of Birmingham's belief in themselves was not really tested by a Chelsea side that failed to hit the high notes.
Birmingham certainly played with more determination in the opening spell as they strived to take the game to Chelsea.
It was significant that they maintained a clean sheet in the opening exchanges and their relief was reflected with a more promising performance.
Out of form Emile Heskey was sadly at fault with a poorly directed header from Jermaine Pennant's free-kick.
Olivier Tebily, standing in for the injured Mario Melchiot, produced the kind of threat needed to put Chelsea out of their stride when he moved forward menacingly to fire a goalward shot which Petr Cech flicked over the bar.
Arjen Robben, returning from a three-match ban, was obviously out of favour with the Birmingham fans when a reasonable tackle from Pennant resulted in the Dutchman making a somewhat spectacular dive.
With Pennant voicing his objections Chelsea took a quick free-kick and Robben moved in to shoot from close range only for Taylor, who had conceded ten goals in Birmingham's previous three games, to block the effort.
The longer Birmingham maintained a clean sheet the more they gained in confidence but there was always the ominous feeling that Chelsea were playing well within themselves.
Frank Lampard and Damien Duff were both powerful workers, while the threat of Robben was always hovering around.
Eidur Gudjohnsen came more into the picture near the break as Chelsea slowly stepped up a gear to break Birmingham's spirit.
The Londoners certainly made more impact in the second period as they attacked at depth to expose Birmingham's limitations.
But manager Jose Mourinho was far from happy with the performance and that was reflected by his decision to send on his three substitutes, Crespo, Joe Cole and Michael Essien in the space of four minutes.
With two defeats in three of their previous three away games Chelsea are obviously struggling to find their form on the road.
Birmingham were able to benefit from this latest below-par performance as they collected a valuable point which could be the inspiration for their survival.