First-half goals by Cristiano Ronaldo (two) and Carlos Tevez made it a stroll in the sun for United.
The one dark cloud came with the 37th minute dismissal of Nani.
After falling over attempting an acrobatic kick, the Portuguese winger was shown the red card by Mike Riley when he appeared to butt Lucas Neill as the Australian tried to pull him to his feet.
United were left to play almost an hour with only ten men, but the Hammers failed to capitalise on their advantage.
The Reds enjoyed the perfect start with a goal in the third minute.
United goalkeeper Edwin Van der Sar's kick came off the head of West Ham's James Tomkins when he went up with Nani.
It fell to Ronaldo on the right and he cut into the West Ham box from the wing, leaving Neill in his wake, before scoring with a low right-foot shot from 12 yards.
West Ham almost equalised four minutes later when United made a hash of clearing Scott Parker's corner.
Tomkins nodded the ball on to Bobby Zamora, whose header was hacked clear by Patrice Evra and Rio Ferdinand.
United made it 2-0 after 24 minutes when Ronaldo scored his second and probably the luckiest of his 40th goal in all competitions and 30th in the league this season.
Owen Hargreaves' cross form the right corner of the penalty area bypassed a wall of defenders and went in off Ronaldo's right thigh from close range at the far post.
The third and best of United's goals came two minutes later.
Ronaldo's cross from the left inside to Tevez saw the Argentinian take the ball in his stride before hitting a ferocious right-foot 30-yard drive over goalkeeper Robert Green and into the roof of the net.
West Ham reduced the areas two minutes later.
Bobby Zamora's cross from the right was headed up in the air by United defender Wes Brown and Dean Ashton scored with a spectacular overhead kick from 10 yards out at the far post.
But any doubts about the result were ended in the 59th minute when Michael Carrick picked up a loose ball midway inside the West Ham half and was allowed to run on before scoring with a right-foot shot from 20 yards which was deflected in off the hapless Neill.
United could have had a fifth when Darren Fletcher's 71st minute shot cannoned back of a post.
The chance set up following good work from Evra and substitute Ryan Giggs.