Albion are level with the Bluebirds in Cardiff after taking an early lead through man of the moment Lewis Dunk.
Dunk headed in a Solly March free kick.
Callum Paterson equalised for the home side, from close range, on the half hour.
But he game changed for the Seagulls when Dale Stephens was shown a straight red card for his challenge on Gregory Cunningham on 34 minutes.
Yves Bissouma replaced Solly March soon after.