United entered the match four points adrift of the second-from-bottom Wearsiders, and knew that a win for Sunderland on the night would see the Red Devils relegated.
United were without the services of forward Joshua Bohui due to a hamstring problem, but the home side started well, and took the lead in the 23rd minute courtesy of a smart finish from the highly-rated Netherlands youngster Tahith Chong.
Sunderland would have been looking to gain a foothold early in the second period, but United put the match beyond them in the 55th minute when Indy Boonen found the bottom corner with a smart finish.
The home side then had their fourth on the hour when Joe Riley's left-footed effort from the edge of the box curled into the corner of the net.
The victory has moved United to within one point of 11th-placed Sunderland, and now just two points off Tottenham Hotspur Under-23s in 10th position.
MAN UNITED U23s (4-2-3-1): O'Hara; Riley, R. Williams, Borthwick-Jackson, O'Connor (Warren 71'); Redmond, Hamilton; Chong (Kehinde 67'), Gribbin, Boonen (McIntosh-Buffonge 76'); Dearnley
SUNDERLAND U23s (4-4-2): Stryjek; Gamble, Hume, Mumba, Taylor; Storey, Molyneux (Mbunga Kimpioka 46'), Embleton, Connelly (Wright 63'); Shields (Bale 69'), Diamond