The Red Devils finished sixth last season, largely due to their home form, and qualified for the Champions League by winning the Europa League.
Substitute Anthony Martial made it 3-0 in the 87th minute with a side-foot finish after being played in, again by Mkhitaryan. Henrikh Mkhitaryan's free-kick from the left hung high in West Ham's box but there was only one man likely to meet it, with Lukaku's simple header sending the ball past Hart and into the bottom-right hand corner. He took so much, mostly unjust, criticism last season.
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A source close to Mr Davis said the papers would highlight the British teams were "on the front foot" in the negotiations. The first will be a proposal for new customs arrangements.
And the Armenian made it two assists for the day a few minutes from time as he played in substitute Anthony Martial with a attractive first-time pass. Mourinho expectedly gives the Old Trafford debut to Romelu Lukaku, spearheading an attacking lineup that includes fringe starters Marcus Rashford and Juan Mata.
Man Utd have now won more opening game fixtures (17) than any other side in Premier League history. West Ham lose the ball with Obiang and Rashford breaks.
Maraoune Fellaini replaced Mata for the final quarter-hour, while Martial came on for Rashford and Aaron Cresswell took over from Masuaku.
While silverware was added to the trophy cabinet with success in the EFL Cup and Europa League, boss Jose Mourinho knows that far more will be required in the top flight in his second term at the helm. There have been plenty of reasons for United's league struggles; this year, however, everyone at the club will at least expect them to challenge for the title for the first time since Sir Alex Ferguson retired.