Any win over the rivals from Merseyside is a sweet one but the task was made easier by the 25th-minute dismissal of Suso for kicking out at Paul Pogba. The Reds were patient before ramming home the advantage after the interval as Will Keane, birthday boy Jesse Lingard and Mame Biram Diouf (2) all got on the scoresheet.
A knock to captain Darron Gibson towards the end of the first half was a worrying note amid the injury problems at first-team level in midfield but it facilitated Lingard's arrival on the day that he turned 19.
In a scrappy opening, the final touch deserted the Reds with Federico Macheda's prod going through to keeper Martin Hansen ahead of Diouf. Nathan Eccleston curled wide at the other end after good work by Raheem Sterling but United just about had the edge.
An incredible run by Diouf ended with a mishit pass that looped to Hansen and Will Keane dragged a shot wide following a positive run by Marnick Vermijl into the box. A driving charge by Macheda then forced a simple save out of Hansen before the game's major talking point.
Spanish winger Suso clashed with Pogba and appeared to kick at the Frenchman's face after falling to the ground. Following consultation with his assistant, referee Ben Toner showed a straight red card - to the anger of the visitors. With the Merseysiders down to 10 men, United look to press home the advantage but Stephen Sama beat Diouf to a loose ball after an intelligent pass by Pogba and Larnell Cole lashed over from a difficult angle.