Craig Gardner’s extra-time winner sent Birmingham into a Carling Cup final clash with Arsenal at the expense of West Ham.
Gardner’s goal handed City a 4-3 aggregate win, after Carlton Cole seemed to have set the Hammers on their way with a half-time lead.
But Lee Bowyer and Roger Johnson levelled the tie inside ninety minutes before boyhood Blues fan Gardner struck to complete the comeback.
With both sides entrenched in an English Premier League relegation struggle, the distraction of a cup final appearance ensured an exciting evening.
West Ham settled quicker than their hosts, who displayed early signs of big-stage nerves in front of their own expectant fans.
Birmingham were punished for a poor first-half showing when Gardner and Barry Ferguson let a harmless throw in from the left run between their bodies, allowing Cole ample time to curl a glorious right foot shot around Ben Foster from 25 yards.
The tie was almost out of sight six minutes later when Zavon Hines met Mark Noble’s left-wing free kick and sent an acrobatic overhead effort past Foster that clipped Birmingham’s post.
After that, however, West Ham faded.
Worried by their impotency up front, Blues boss Alex McLeish threw on Nikola Zigic for the second half and the giant Serbian teed up Gardner, who could only watch in disbelief as his half-volley struck the foot of Robert Green’s post.
Birmingham were suddenly a far more direct and dangerous proposition and they finally dragged themselves back in to the tie on the hour mark when Bowyer smashed home a thunderous drive from the edge of the area that Green never had any hope of stopping.
And the Hammers goalkeeper was powerless again 11 minutes from time as Bowyer’s corner was met by Roger Johnson’s powerful header from six yards out.
Green’s brilliant finger tip save touched Gardner’s pile driver on to the post with just seconds of the ninety minutes remaining.
But just four minutes in to extra time, Gardner scored the tie’s winner with an assured finish from just outside the area to take Birmingham to within one win from repeating their 1963 League Cup triumph.