ERIC BAILLY scored only the second goal of his career – and first for United – as Jose Mourinho’s side battled their way to another victory.
Romelu Lukaku, Paul Pogba and Anthony Martial then scored in the final 10 minutes as the Swans fell apart with embarrassing ease.
United were anything but convincing but in a disappointing game but they went on the rampage at the end with three goals in the space of four minutes.
Unchanged from the 4-0 win over West Ham, United were lucky not to concede after just three minutes when Jordan Ayew sent an effort against the bar a rare mistake from Eric Bailly.
At the other end, United also tested the woodwork courtesy of Phil Jones’ header from Juan Mata’s free-kick.
Paul Pogba was lucky to stay on the pitch after he was booked for a foul on Tom Carroll before then delivering another rough challenge on Martin Olsson. He was given some stern words from ref Jon Moss.
Marcus Rashford found himself clean through but toe-poked the ball straight at Lukasz Fabianski and Mourinho’s team were stuck in third gear – but they opened the scoring in the 45 minute.
Daley Blind’s corner was met by a powerful header from Pogba, Lukasz Fabianski did well to make contact with the effort and the ball smacked against the underside of the bar.
Yet Bailly was first to react and stuck his leg out to give United the edge. They were not any better in the second period but they did not need to be.
Swansea did not create enough although Tammy Abraham headed over and the hosts failed to turn in a decent corner from Tom Carroll.
Lukaku struck after Anthony Martial and Mkhitaryan combined and Pogba made it 3-0 by lifting the ball over Fabianski. Sub Martial then drilled the ball into the corner for the fourth.