The 26-year-old Venezuela striker controlled Sebastien Pocognoli's cross from the left before burying the ball into the left corner on 67 minutes against an increasingly toothless United, who had lost Juan Mata to a second yellow card on 26 minutes.
The Spain international was booked for not retreating and blocking a quickly-taken free kick before receiving his marching orders two minutes later for kicking Darren Fletcher's shin in a clumsy tackle.
“You know the first one is a stupid yellow card and then you have to be aware the referee can give a second yellow card,” United manager Louis van Gaal told BBC Sport.
“A referee has to decide within one second but when you know the player, Mata never hurts a player.”
United's first league defeat at The Hawthorns since 1984 kept them sixth in the table, three points behind Manchester City in fourth, while West Brom climbed to 11th on 39 points with a third win in four league games.
“Second half we were definitely off the pace a bit but the goal was a smashing finish,” said West Brom manager Tony Pulis.
“It has taken him time to settle in and he has had ups and downs but they love him to death here.
“The most important thing is the next game, as you've seen this year, results have been off the radar. Let's get 40 points, I think that's definitely safe.” – Reuters
Original source: Huge setback for United’s top four hopes