Marcus Rashford bagged a brace after he opened the scoring for Manchester United as he cooly fired his penalty into the top left-hand corner past Kepa Arrizabalaga in the first-half. He then placed it into the back of the net on a counter-attack. Anthony Martial and Daniel James also got on the scoresheet for the Red Devils.
Ole Gunnar Solskjaer started his new summer signings Aaron Wan-Bissaka and Harry Maguire against the Blues, with Dan James having to settle for the bench.
Meanwhile, Frank Lampard made the call to start both Ross Barkley and Mason Mount in the midfield, with Christian Pulisic having to start on the bench.
N'Golo Kante wasn't deemed fit enough to start at Old Trafford, so Mateo Kovacic and Jorginho were selected in the midfield pivot for the visitors.
Chelsea had an extremely bright start and were inches away from taking a lead. Tammy Abraham pounced on a loose ball and struck a fine effort past David De Gea, but the woodwork denied thee forward scoring on his Premier League debut.
All of Frank Lampard's side hard work could have been lost when Kurt Zouma misplaced a pass. Pressure from the hosts saw Zouma pass it into an open space, ended up in the path of Anthony Martial. He cut in, and curled a poor effort into the hands of Kepa Arrizabalaga.
Chelsea nearly then went ahead after Azpilicueta played a fantastic ball across the face of goal but neither Mount nor Abraham could latch onto it.
The hosts did take the lead from the spot after Kurt Zouma made a clumsy foul in the box. Rashford stepped up, and converted into the back of the net to give United the lead against the run of play.
After the break, Emerson was the next to be denied by the woodwork as the Blues seemed a leveller, but it was Manchester United who drew second blood. The hosts had a quick counter-attack, and Anthony Martial was on the end of a cross into the box, and the Frenchman tapped home to double their lead.
Two quickly became three as 17 seconds from the restart it was 3-0. A disaster. An excellent ball from Paul Pogba found Marcos Rashford and he calmly put it past Arrizabalaga.
N'Golo Kante was then brought on to replace Jorginho late on to get minutes under his belt after returning from injury, but United still managed to grab a fourth in the final stages at Old Trafford.
New signing Dan James scuffed his effort past Arrizabalaga to score on his debut and make sure that there was no coming back from Frank Lampard's side.
An extremely disappointing result from Chelsea, with four defensive errors resulting in four goals. A lot of work to do to improve, and Frank Lampard will be the first to admit that.
On an afternoon which promised so much. The first-half matched the excitement, but it dwindled away into a poor day for Chelsea.