Many new faces were handed their first Premier League starts with their new teams in the final fixture of the opening weekend. West Ham's four recruits were in the lineup, while Lukaku and Matic also played from the start at Old Trafford.
And it did not take long for Manchester United to claim complete control of the match. The hosts gradually began to push the Hammers back into their own half, with Bilic's side unable to make any inroads going forward.
Mata was involved in United's first clear chances, firstly when his close-range shot was blocked by De Gea and secondly when he unselfishly looked to square for Lukaku rather than score himself and the ball was eventually cleared.
With the Hammers pinned inside their own box, it was only a matter of time before Mourinho's men found a breakthrough. Lukaku got off to a flying start at the Theatre of Dreams, scoring his first goal after thirty-three minutes.
Rashford ran at the defence down the middle before slipping a clever through ball for the Belgian, who smashed his finish in off the post.
West Ham managed to show some signs of improvement by edging closer to De Gea, but it was not until the final minute of the first half that the Spanish keeper was troubled. Good build-up play saw Fernandez unmarked at the edge of the box and the midfielder's powerful strike was straight at the keeper who simply punched it away.
With West Ham's gameplan of sitting back and frustrating Mourinho's side proving ineffective, Bilic attempted to urge his side to go forward, but the second half kicked off in similar fashion.
Rashford fired a warning shot wide before Lukaku grabbed his second of the afternoon. Mkhitaryan clipped in a cross from the left and the Belgian got ahead of Masuaku to head the ball into the bottom corner.
Arnautovic tried to get his team back into the game, but his header was tipped over the bar by De Gea. As the minutes went by, the Hammers seemed to resign to fate with the home side beginning to enjoy themselves.
Lukaku had the chances to complete a hat-trick, but it was not to be. Rashford, also in search of a goal to open his tally for the season saw his curling strike bounce off the base of the post.
The striker put on a lively display, despite failing to get on the scoresheet. As the game entered the final 10 minutes, he was replaced by Martial who in turn did manage to beat Joe Hart. Mkhitaryan slipped a brilliant first-time pass for the Frenchman, who slotted the ball into the bottom corner.
Pogba added a fourth to complete a well-merited win for the Red Devils, and to culminate the Hammers' humiliation. The midfielder curled the ball past Hart from 20 yards to make the win even more emphatic.