Maik Taylor and Kevin Phillips were the heroes for Birmingham as they scraped past Brentford with a 4-3 win on penalties after the sides finished 1-1 after extra time.
Brentford silenced the 15,000 strong crowd at St. Andrews with the opening goal on 67 minutes.
Sam Wood fired a smart shot into the bottom of the net past Maik Taylor in the Birmingham goal.
The goal seemed to finally wake Brum from their slumber and the chances began to arrive as the pressure increased.
Perhaps the best of those chances arrived in the 79th minute as a Lee Bowyer corner found Liam Ridgewell in the six-yard box, but the defender could only steer his header harmlessly over the bar.
Just as Brentford fans thought their side had weathered the storm, Kevin Phillips popped up with a late-late equaliser to break their hearts.
The veteran striker punished the visitors for leaving him unmarked in the six-yard box to fire smartly home.
Extra-time beckoned, and cagey football became the order of the day as both sides looked to penalties to settle the affair.
Birmingham went 3-2 up on penalties before Michael Spillane and Lee Bowyer both missed. Lewis Grabban converted for Brentford before Stephen Carr responded for Birmingham.
Craig Woodman had to score to keep Brentford alive, but he saw his spot kick smartly saved by Taylor to condemn Brentford to defeat.