Nikola Zigic salvaged a stoppage-time point for Birmingham thanks to Tomasz Kuszczak's howler as Brighton's play-off aspirations suffered a blow.
It was the third time this season the Serb has rescued a point, as Kuszczak let the ball through his hands.
Steven Caldwell headed the hosts in front but the Seagulls levelled courtesy of Ashley Barnes' strike.
David Lopez volleyed what looked to be the winner before half-time only for Zigic to equalise late on.
Even then, Brighton could have nicked it, but Blues' sought-after goalkeeper Jack Butland produced a wonder save to keep out Dean Hammond.
Brighton will feel like it is two points dropped having looked set for their first win over Birmingham in eight attempts since 1989 and only their second ever success at St Andrew's.
And the visitors' late set-back has seen them drop five points behind the top six, despite moving up one place in the Championship table to eighth.
Cash-strapped Blues have just one win in their last 10 games and they remain in 20th spot - five points clear of the relegation zone.
Following a tentative start an unmarked Caldwell met Rob Hall's corner after 18 minutes to power a header past Kuszczak.
Yet the visitors levelled in the 24th minute. Andrea Orlandi broke down the left and cut a ball back for Barnes who fired into the bottom corner from 20 yards.
Chris Burke, who netted the winner a 1-0 triumph for Birmingham in the reverse fixture earlier this season, was thwarted by a fine parried save from Kuszczak just before half-time.
And the stop proved crucial as Brighton claimed the lead in the 43rd minute with Wayne Bridge sending over a great cross to Lopez, who volleyed under Butland.
Zigic came on at half-time and the giant striker looped a header over before he sealed an unlikely point.