Man U inflict biggest PL defeat over Chelsea for 54 years
United were not at their best against Frank Lampard's side but they proved lethal in front of goal, with strikes from Marcus Rashford (2), Anthony Martial and Daniel James enough to secure all three points.
The last time the Red Devils beat Chelsea by such a big margin was in March 1965 under Matt Busby, when they also won 4-0. As well as suffering the joint-heaviest defeat of his brief managerial career to date, Lampard was dealt the biggest reversal by a Chelsea boss in their first game in charge since Danny Blanchflower oversaw a 7-2 loss at Middlesbrough in December 1978.
The defeat also means Chelsea will end a day in the Premier League relegation zone for the first time since September 2000.