Manchester United avenged their September defeat to Albion to increase the pressure on Baggies boss Pepe Mel on another miserable day at The Hawthorns.
Phil Jones’ first-half header gave United a 1-0 half-time lead and Wayne Rooney and Danny Welbeck added goals after the break as David Moyes’ side ran out comfortable winners.
Mel is now without a win in seven games in charge and, after a turbulent two weeks behind the scenes, the limp second-half display from his side is unlikely to silence speculation about the Spaniard’s future.
Albion showed some signs of promise in the first half but the belief drained from Mel’s men once they fell behind.
And to add to his woes, Claudio Yacob, Steven Reid and captain Chris Brunt all went off injured.
Albion had a nervous moment early on when a backpass from Chris Brunt bounced over the foot of goalkeeper Ben Foster and ran for a corner, but fortunately the flag kick came to nothing.
There was also some early encouragement for the Baggies, however, when Victor Anichebe powered away from Chris Smalling and burst into the box, only for the United defender to get back and make a vital challenge.
United had another near-miss when a Wayne Rooney corner was headed by Marouane Fellaini and turned goalwards inadvertently by Brunt, forcing Youssouf Mulumbu into a crucial goalline clearance.
The first effort on target came in the 29th minute when a left-wing cross by United youngster Adnan Januzaj was headed at the far post by Rafael, with Foster producing a fine reaction to push it onto the crossbar.
But the deadlock was broken on 34 minutes thanks to some poor defending from the Baggies.
Liam Ridgewell was beaten two easily by Rafael, forcing Brunt to foul the full-back on the edge of the box.
And the hosts then handed Jones a free header as he sent Robin van Persie’s free-kick thundering past Foster.
Albion might have equalised just before the interval when substitute James Morrison, who had just replaced Claudio Yacob, fed Anichebe with a good, low pass.
The striker held off Jones but dragged his shot just wide.
Moments later Foster suffered another scare when he misjudged a high clearance under pressure from Juan Mata and saw the ball bounce up and hit his hand outside the box.
United screamed for handball but the officials did not oblige.
Eight minutes into the second half Albion unlocked the United defence as Zoltan Gera exchanged passes neatly with Anichebe in the United box.
But the Hungarian’s touch was heavy and David De Gea gathered.
There was then major controversy as Van Persie somehow escaped a red card.
Moments after being booked for a tackle from behind, the Dutchman committed a late challenge on Steven Reid that seemed certain to earn him a second yellow card but referee Jonathan Moss let him off with a warning.
Albion continued to build up a head of steam and went close when Anichebe used his strength to turn in the box and aim a low cross towards Brunt at the far post, but Mata made a vital interception.
But the Baggies suffered another double-blow when both Steve Reid and Brunt were forced off injured.
Stephane Sessegnon replaced Reid but, with the hosts reduced to 10 men temporarily after Brunt limped off, United doubled their lead.
Rafael produced a fine cross from the right and the unmarked Rooney headed home at the far post on 65 minutes.
That goal killed what had been a cracking Hawthorns atmosphere and deflated Albion, who struggled to make an impression on the United rearguard, with Anichebe blasting well over from the edge of the box in the final 10 minutes.
And the scoring was complete with seven minutes remaining as the Baggies were unlocked by Rooney’s through-ball and Welbeck produced a fine, curling finish to beat Foster.