Rasmus Hojlund made it four Premier League goals in as many games and Alejandro Garnacho scored twice as Manchester United recorded their biggest home league win of the season to move back into the top six against West Ham at Old Trafford.
Hojlund provided the smart 23rd-minute finish to set the hosts on their way to victory.
Garnacho's deflected effort doubled their advantage less than a minute after West Ham full-back Emerson wasted a glorious chance to equalise. The Argentine added another near the end after Scott McTominay seized possession inside the West Ham half.