Hosts West Ham knew they were up against an in-form team, and their task was made all the more difficult after referee Mike Dean sent off Sofiane Feghouli for a contentious foul just 15 minutes in.
United understandably bossed possession thereafter, and were unfortunate not to be in front on 35 minutes as Antonio Valencia was denied by goalkeeper Darren Randolph from close range, with Jesse Lindgard’s rebound hitting the post.
Manuel lanzini forced a fine save from David De Gea late in the first half, with the Spanish shot-stopper at his best once more on the hour mark to deny Michail Antonio one-on-one.
United kept creating chances themselves however, with their two second-half substitutes combined with the perfect result: Marcus Rashford’s trickery out wide left the Hammers’ defenders for dead, tee-ing up Mata who slotted home to give the visitors the lead on 63 minutes.
With their tails up, the Red Devils pushed for a second, Paul Pogba coming close twice, yet firing wide on both occasions.
Not so for Zlatan Ibrahimovic however, as a bobbing ball fell kindly for the Swede who reacted quickest to volley in his side’s second to double the lead.
That’s how it would end, as United secure maximum points yet remain in ffith, with rivals Tottenham Hotspur – on level points – up against table-topping Chelsea on Wednesday.