As bad as United were though, Brighton were terrific and full value for the comprehensive scoreline.
Moises Caicedo opened the scoring after 15 minutes when he drilled a low effort past David De Gea from 25 yards out.
It appeared Graham Potter told his side to go for the jugular during the break and they did just that, doubling the lead in the 49th minute when Leandro Trossard pulled back for Marc Cucurella to blast into the roof of the net.
Eight minutes later there was another goal, the pick of the bundle, when Cucurella brought down a fantastic long pass from goalkeeper Robert Sanchez, then found Trossard in the box. He slid a ball through to Pascal Gross who calmly pushed the ball past the sliding Raphael Varane with his right foot, before sliding home with his left.
Unbelievably, the lead was four just before the hour mark when former Red Devil Danny Welbeck lofted a ball over De Gea and Diego Dalot’s goal-line clearance was deflected over the line by Trossard – whose performance certainly deserved a goal.
The result means United will end the season with their worst points tally ever in the Premier League under the 64 accumulated in 2013-14, they currently have 58, and could yet slip to the seventh place they finished in under David Moyes.
Brighton rise to ninth and look set for the first top-half, top-flight finish in their history.