The Red Devils were simply a cut above the Hammers. Romelu Lukaku opened the scoring with his first league goal for the club and he doubled his tally in the second period with a header.
Substitute Anthony Martial added a third before Paul Pogba rounded off the scoring with an excellently taken fourth.
It is a victory that puts Manchester United top after the opening round of Premier League fixtures. Jose Mourinho will hope his side stay there for the remainder of the campaign.
Here are the five things we learned from United's victory over the Irons.
No happy Premier League return for Hart
Back in the Premier League after a season on loan with Torino in Serie A, England's No.1 would've wanted to make a point on his return to English football.
Hart's first involvement in the game was to misplace a pass, across Manchester you wouldn't have been surprised if there was a wry smile from Pep Guardiola.
Playing out from the back is not Hart's strength, shot-stopping is. And he did well in the opening period to come off his line and deny Juan Mata.
However, there was to be no clean sheet for Hart as Lukaku opened the scoring in the 33rd minute. It was an excellent finish from the hulking striker. Hart had no chance and it was a similar story for United's next two goals.
He may feel he could've done more to deny Pogba's late fourth but it was a fine strike from the Frenchman and compounded a disappointing return to the Premier League for Hart.
Masuaku isn't a capable deputy
The French defender was signed from Olympiacos last summer for £6million and started at Old Trafford because of Aaron Cresswell's hamstring injury.
It was an opportunity for Masuaku to impress. Instead he did the opposite. The 23-year-old struggled throughout the game and never looked comfortable when West Ham did have possession.
He was at fault for Manchester United's second goal by not staying close enough to Lukaku from a free-kick. And subsequent replays showed the left-back having a joke with the Belgian before the cross came into the penalty area.
His final action of the match was to let a simple pass roll under his foot. Seconds later Cresswell was introduced despite not being fully fit.
It was a telling change from Slaven Bilic and it wouldn't be a surprise if West Ham enter the transfer market for another full-back.
Matic has rediscovered his mojo
When Matic completed a £40million move to Old Trafford from Chelsea, there weren't many Blues fans who were disappointed with the fee their club had received.
While the Serbian was an important player in last season's title win, he was far from faultless. And his lethargic display in the FA Cup final frustrated many a Chelsea supporter.
But a move to Manchester United has reinvigorated the 29-year-old, who seemingly stagnated at Stamford Bridge.
He looked back to his best, patrolling midfield powerfully and keeping possession ticking over. He even went on one mazy run in the first half that former team-mate Eden Hazard would've been proud of.
It was his interception that led to United's opening goal and with the ball he completed 85.5 per cent of his passes.
You only wonder what Chelsea fans watching the contest must have been thinking.
No dream debut for Hernandez
Before the game ‘The Little Pea' spoke fondly about his five years at Manchester United.
Hernandez won two Premier League titles during his time at Old Trafford and scored the last goal of the Sir Alex Ferguson reign, so was understandably looking forward to returning to “his house”.
The Mexican admitted that he wasn't sure if he'd celebrate if he found the back of the net. Unfortunately for the 29-year-old, he didn't have the opportunity either way.
Hernandez has the fifth best goals to minutes ratio in Premier League history, behind some of the Premier League's best ever strikers in Ruud van Nistelrooy, Harry Kane, Sergio Aguero and Thierry Henry, but was starved of service at Old Trafford.
His only sight of goal came late into the game but he blazed it over. His work-ethic was admirable, however.
Lukaku the bully United needed
The powerful Belgian would've wanted to make an immediate impact on his first appearance as a Manchester United player. And, if he could've picked any team to be facing, it would've been West Ham.
Lukaku scored nine times for Everton in ten games against the Hammers. So he would've been confident of opening his Premier League account for the Red Devils.
And, after a quiet opening half hour, that's exactly what the 24-year-old did. Marcus Rashford surged forward, slipped a pass behind the West Ham defence and there was Lukaku, who finished confidently.
The goal put United firmly in control. The striker would double his tally in the second half and the Red Devils won the game comfortably.
Last season United's inability to break down weaker teams at home proved their downfall. Zlatan Ibrahimovic was a fine striker but he wasn't always the most clinical.
Lukaku is a different animal. He has been called a flat-track bully in the past but that is exactly what Manchester United. He should prove a huge success at Old Trafford.