Wayne Rooney sparked Manchester United into life against a limited West Brom as the champions moved ominously up to fourth in the Premier League table.
The visitors battled hard early on while Rooney had an effort disallowed.
But the in-form England international cut inside Ryan Donk to fire a superb opener on 55 minutes before setting up Cristiano Ronaldo for a simple second.
Dimitar Berbatov added a casual third after poor Baggies defending before Rooney set up Nani to slide in late on.
With perennial rivals Chelsea, Arsenal and Liverpool all winning and United sitting in eighth prior to the late kick-off, the home side were under a degree of pressure to get a win which would really kick-start their league campaign.
