Paul Scharner's second-half goal earned West Brom their first away league win over 10-man Aston Villa for 32 years.
Villa went ahead through Darren Bent's penalty but this Barclays Premier League game turned Albion's way after midfielder Chris Herd was red-carded after 35 minutes following a clash with Jonas Olsson inside his own box.
Chris Brunt missed the spot-kick but the Baggies cashed in on Villa's frailty at set-pieces with Olsson equalising before half-time and Scharner netting the winner - both from Brunt corners.
It would be fair to say referee Phil Dowd will not be on the Christmas card list of Villa fans after dismissing Herd.
They still remember Dowd's decision not to dismiss Manchester United defender Nemanja Vidic for hauling back Gabriel Agbonlahor during the early stages of the 2010 Carling Cup final.
But victory completed a quickfire derby double for Albion after last week's triumph over Wolves and they have collected 11 points from the last six games.
They overcame the early loss of striker Shane Long through injury and dominated the second half with their numerical advantage and were more inventive with their passing.
Scharner impressed as the midfield enforcer while Somen Tchoyi was a handful for the Villa back four after replacing Long.
Bent squandered a golden chance to put Villa ahead after five minutes.
Barry Bannan failed to make proper contact on his shot but it fell straight to the feet of Bent unmarked eight yards out. The England striker looked certain to score but scooped his shot over the crossbar.
Alan Hutton was booked for a touchline tackle on Long who was replaced after 20 minutes by Tchoyi.