Rooney then extended United's advantage with 33 minutes played as he prodded home from close range after the hosts had failed to clear their lines.
Here, Sports Mole takes a closer look at the action between the two teams at Upton Park
On target: 1
On target: 7
Was the result fair?
Manchester United were good value for the win in the end thanks to a display that was lethal in attack and stoic in defence. West Ham made a go of it in the second half, but they lacked ideas and struggled to break their opponents down.
West Ham's performance
The Hammers were routinely torn apart in the first half as Man United played some clinical attacking football. Sam Allardyce's side were caught out numerous times at the back, with the pace and movement of the champions proving too much. There was an improvement after the break as West Ham played to their strengths, but they continued to huff and puff without much luck in the final third. Three defeats on the spin now mean that the East Londoners are not yet safe from relegation.
Man Utd's performance
The Red Devils were rampant during the opening 45 minutes as Wayne Rooney, Juan Mata, Shinji Kagawa and Ashley Young all linked to give the West Ham defence a torrid time. This kind of fluidity has been seldom seen under David Moyes, but on this occasion it worked a treat. While the first half was a showcase for their attacking talents, the second period saw them put a lot of effort into their defensive duties as the hosts bombarded them with some direct football. However, the back four stood up to the challenge, with Michael Carrick looking comfortable as a centre-back alongside Phil Jones.
Sports Mole's man of the match
Juan Mata: The Spaniard was superb for the champions, leading most of their forward play and displaying some wonderfully deft and delicate touches up front. He has been played out of position during much of his time with United, but he looked right at home in the advanced role that he was given at Upton Park, allowing him to create and find space for himself and his teammates.
Mark Noble made a calamitous error leading up to United's second goal as his poor clearance went straight to Rooney, who tapped in. The West Ham midfielder had time and space to whack the ball away from danger, but he fluffed his lines and was made to pay the price.
Lee Mason had one or two contentious calls to make [mostly against West Ham], but this was a sound enough display from the official.
West Ham: The Hammers continue their fight for Premier League survival on Wednesday at home to Hull City.
Man Utd: The Red Devils return to Premier League action on Tuesday when they welcome local rivals Manchester City to Old Trafford.