The £75million striker Lukaku, from Everton, hit home either side of the break as United looked much improved from their disappointing campaign last season.
Jose Mourinho, has praised his new signings, Romelu Lukaku, and Nemanja Matic, after Red Devils’ comprehensive drubbing of West Ham at Old Trafford, Anthony Martial and Paul Pogba rounded off the rout in the closing stages, as United took top spot at the end of the week’s action.
Mourinho spent almost £150m on Everton striker Lukaku, Chelsea midfielder Nemanja Matic and Benfica defender Victor Lindelof this summer in a bid to achieve it.
Jose Mourinho’s team were a constant threat against a poor Hammers side, offering excitement and encouragement to their supporters on the opening weekend of the new Premier League season.
BBC Sport report That, The Belgium international doubled the lead after half-time, glancing in a header from Henrikh Mkhitaryan’s inswinging free-kick.
United teenager Rashford curled against the inside of Joe Hart’s left-hand post before substitute Anthony Martial ended the match as a contest with a slick finish.
There was still time for a fourth, however, as Paul Pogba curled in from distance.
The Hammers offered little going forward in a passive performance, although new signing Marko Arnautovic did flick a header onto the top of the home crossbar at 2-0.
The Red Devils have now lost only one of their 14 opening-day Premier League fixtures at Old Trafford, while West Ham’s season began with a record 11th defeat.
West Ham Manager Slaven Bilic said afterwards it was hard to find any positives, but one poor performance on the opening weekend does not mean the Hammers should necessarily panic, especially as several key players – including Manuel Lanzini, Andy Carroll and Michail Antonio – were missing through injury.