Two goals on debut for Romelu Lukaku were added to by late strikes from Anthony Martial and Paul Pogba as Jose Mourinho's side surged to the top of the Premier League.
Nemanja Matic also impressed on debut as the Red Devils recorded their biggest win in three years.
Nemanja Matic - Bargain
The Serbian midfielder looked a touch on the expensive side when he arrived in Manchester, £39 million for a 29-year-old looked questionable business. But in the process of weakening current champions Chelsea and strengthening their own midfield, United may have pulled off one of the deals of the summer. His imperious midfield display gave Pogba the freedom he needed to influence the game going forward.
This is Paul Pogba's year
After a decent first year at United, the Frenchman needs to kick on and really show why United paid a then world record £89 million for his services. The arrival of Matic is sure to lessen Pogba's defensive work throughout the season, and free him up to attack. His passing range was obvious to see on Sunday, teeing up Juan Mata with a wondrous pass, as well as finishing from well outside the box to complete the rout.
Pace and Power - The new formula
Since the retirement of Sir Alex Ferguson, Manchester United's squad has consisted of highly technical but not very physical players, which has cost them finishing anywhere above fourth since the Scot's departure. Mourinho has now built a squad that is far more physical than has been seen in recent years, with the likes of Pogba, Matic, Marouane Fellaini bossing the midfield, Romelu Lukaku and Eric Bailly also providing huge size. There's an abundance of pace as well, Lukaku and Pogba recorded the highest sprint speeds of the weekend, with Anthony Martial and Marcus Rashford not far behind.
Long way to go for Lindelof
While two of United's new signings excelled on the opening day, one was nowhere to be seen. Victor Lindelof wasn't included in the matchday squad, despite playing in the UEFA Super Cup against Real Madrid. Mourinho has said he will keep the faith with the Swede, but admits he's not ready for Premier League action, and he only played him against Los Blancos as Bailly and Phil Jones were suspended.
Mourinho has faith in Jones
Despite several injury-plagued years at United, it appears Mourinho has sufficient faith in Phil Jones to make him his first-choice centre-back this season. With Marcos Rojo injured and Lindelof not ready, Jones is fighting Chris Smalling for the right to start alongside Bailly at the back, and it looks like he's won. A very solid display against the Hammers looks to solidify his place in the side for the trip to Swansea City on Saturday.