By Rob Bishop
Villa tasted defeat at the hands of Albion for the first time in more than a quarter of a century on an afternoon to forget at The Hawthorns.
Despite the boost of a fourth minute own-goal by Abdoulaye Meite, Gary McAllister's men were pegged back by a 60th minute Peter Odemwingie equaliser.
And although the Baggies then had Paul Scharner sent off for a second bookable offence, Youssouf Mulumbu pounced seven minutes from the end to condemn Villa to their first setback at the hands of their neighbours since 1985.
The result was all the more disappointing in that it ended a four-match unbeaten run in which Villa had all but secured Barclays Premier League safety - and it came after such a promising start.
If there was ultimately a touch of fortune about the opening goal, there was certainly no disputing the quality of the build-up.
Stewart Downing won possession to thread a fine pass through to Gabby Agbonlahor and when the ball was returned to Downing, he cut inside his marker to deliver a knee-high cross from the right.
Meite stuck out his right leg in an attempt to clear but succeeded only in putting the ball past Scott Carson and into the bottom corner.
There might easily have been a second Villa goal a few minutes later, Stiliyan Petrov unleashing a fierce low shot which Carson initially fumbled before grabbing the ball at the second attempt as Darren Bent moved in for the rebound.
Albion were clearly rocked by the visitors' bright start and almost 19 minutes had elapsed before Roy Hodgson's men produced their first serious goal attempt, although it nearly brought them an equaliser.
A delightful four-man move ended with Mulumbu letting fly with a powerful rising 25-yard drive which was heading for the top corner until Brad Friedel flung himself to his left to tip away for a corner.
That was followed by a fine Simon Cox pass which released Carlos Vela into the penalty area.
The midfielder managed to chip the ball over Friedel but his angled effort was comfortably over the bar.
As Villa began to press forward again, Nigel Reo-Coker played the ball across the edge of the penalty area for Downing to cut inside Nicky Shorey and fire a low drive wide of the near post.
Then a lightning counter attack saw Downing set up the overlapping Kyle Walker for a dangerous cross which Carson pushed over with some difficulty before Bent netted from close range but was ruled offside.
A Vela free-kick which was just too high was the final significant action of the opening period, although Villa were quickly back on the offensive after the break, Petrov sending a low cross just behind Ashley Young and Downing blasting a free-kick into Albion's defensive wall.
But after Friedel had done well to hold Scharner's header, the home side were level on the hour.
James Morrison's deep free-kick from the right was headed back across goal by Jonas Olsson and with Villa unable to clear, the ball eventually fell perfectly for Odemwingie, who volleyed into the roof of the net from three yards.
Two minutes later, Scharner was shown a second yellow card after bringing down Petrov and with the home side down to 10 men, Villa again pressed forward in numbers.
Ashley Young saw a tremendous angled drive pushed away for a corner by Carson, Agbonlahor's 15-yard shot was charged down and substitute Robert Pires made an excellent run that set up Downing for a powerful shot from just outside the area.
Once again, however, Carson was equal to the task, pushing the ball away for a corner - and Albion stormed back to take the lead.
Cox played the ball through to Mulumbu and although Luke Young and Ciaran Clark both made strong challenges, the Baggies midfielder scored with a low shot on the turn from 12 yards.
West Brom: Carson; Olsson, Shorey, Meite, Jara [Tamas]; Morrison, Mulumbu, Scharner, Vela [Fortune], Odemwingie [Tchoyi], Cox. Subs: Myhill, Pablo, Hurst, Miller.
VILLA: Friedel, L Young, Dunne [Clark], Collins, Walker, Downing, A Young, Petrov [Albrighton], Reo-Coker [Pires], Agbonlahor, Bent. Subs: Marshall, Cuellar, Bradley, Delph.