David Moyes was left to rue Sunderland conceding "two poor goals" as the Black Cats returned to the bottom of the Premier League table.
Swansea's shock 3-2 victory at Liverpool put the pressure on the Black Cats before they even kicked off.
The away side could not respond, even though they knew a win could still take them out of the bottom three, depending on results elsewhere.
However, Sunderland were undone by two excellent left-foot West Brom finishes at the Hawthorns as Darren
Fletcher and Chris Brunt struck in the space of seven minutes.
Skipper Fletcher was allowed to control, turn and shoot for the opener on the half-hour while Brunt lashed
home six minutes later after Nacer Chadli had somehow hit the bar instead of the net from six yards.
"It was a tough afternoon, conceding two poor goals," said Moyes. "There were some bit of our football in the second half that were good, but ultimately the goals we conceded cloud everything."
Moyes denied that Sunderland were deflated by the fact they started the afternoon at the foot of the table.
"We can only do what we can do - we can't worry about what anyone else does," he said.
"It's about us trying to get the wins"
"I thought we played better in the second half than the first,. we tried to get forward, tried to pass it better than we had done."
Sunderland showed a measure of improvement in the second half with Jack Rodwell firing over in the 52nd
minute from outside of the box after the best move and possession play by the away side.
Patrick van Aanholt hit the wall from a free-kick soon after and found the home fans with his attempt from the
rebound while his deflected shot was pawed over the bar by Craig Dawson..
A bright move, launched by George Honeyman, ended with Billy Jones having a header comfortably saved by
Dawson and while Moyes threw on Victor Anichebe, the sub, back after a hamstring problem, was unable to
have a positive effect.
"In George I thought we had one of the best players on the pitch, certainly on ours," he said. "We have to take the positive from that.
"It was good to get Victor back on the pitch."