The shake-up seemed to liberate world-record signing Paul Pogba, who led the way with a polished display, heading his first goal for the club on 42 minutes and starting the clever move that led to Juan Mata firing home United's second after 37 minutes.
Mourinho slams football 'Einsteins'
Mata also played a major part in United's third, firing across goal for Marcus Rashford to convert from close range. Chris Smalling had begun the rout with a header after 22 minutes.
Three of the goals came via Daley Blind corners from the left as Leicester headed for their third league defeat.
Rooney dismisses outside criticism
Claudio Ranieri responded by replacing Jamie Vardy and Riyad Mahrez at halftime with substitute Demarai Gray, who scored a stunning goal from 20-yard in the 59th-minute to earn some consolation for the Foxes.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ