Second placed Albion were trailing to an 18th minute strike from Chris Burke when England 'keeper Carson saw red for an amazing attack on the Cardiff striker Michael Chopra.
Carson took exception to an 82nd minute challenge on him by Chopra as the former Liverpool stopper fisted the ball clear.
The duo appeared to exchange words before Carson head-butted Chopra and the culprit began his walk off the pitch even before referee Paul Taylor produced the red card.
That was not the only damage for Albion as Cardiff were also awarded a penalty.
Peter Whittingham saw his spot kick saved by substitute goalkeeper Dean Kiely before the former Aston Villa winger reacted fastest to turn home the rebound for his 14th goal of the season.
It was a thoroughly deserved win for Cardiff, who after a run of three successive defeats, have now put together back-to-back victories.
Burke was their match winner in their previous game against Preston and he put them on the way again after Graham Dorrans and Roman Bednar had failed to convert early chances for Albion.
Cardiff gave then a sign of what was to come when Carson had to tip a rising drive from Gavin Rae over the bar in the 13th minute.
While Rae was out of luck from long range, Burke was more clinical five minutes later when he was released by Kelvin Etuhu.
Albion's defenders made the fatal mistake of backing off and letting the Scottish winger surge forward.
He raced clear before beating Carson with a low 20-yard drive for his fourth goal of the season.
Albion, who crashed to their first defeat in six games, did rally briefly at the start of the second-half with Bednar being denied by David Marshall and Dorrans and Chris Brunt then shooting just wide.
Burke's goal looked to be enough to seal the win before Carson's amazing actions that will cost him a heavy club fine, at least a three-match ban and also possibly his hopes of a place in England's World Cup squad.
External Reports
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West Brom Mad
Cardiff Official Website
The Birmingham Mail
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