Ole Gunnar Solskjaer’s side have struggled for consistency in the opening weeks of the season, but late strikes from Bruno Fernandes, Aaron Wan-Bissaka and Marcus Rashford secured a crucial three points on Tyneside.
But despite the final result, it wasn’t all plain sailing for United as full back Luke Shaw conceded a comical own goal after two minutes.
That setback did serve to sting the visitors into action however, as skipper Harry Maguire powered home from a corner on 24 minutes.
The game swung from end to end before the break as both keepers produced vital stops, with David De Gea denying Allan Saint-Maximin and Karl Darlow saving from Wan-Bissaka.
United did manage to wrestle back control after the break as Fernandes was handed a fantastic chance to put them back in front from the penalty spot.
But the normally nerveless Portuguese international was superbly denied by Darlow.
The Magpies keeper formed a one man barrier in the closing stages before he was final beaten by Fernandes on the stroke of full time.
That goal broke Newcastle’s confidence and United took full advantage in added time.
Wan Bissaka strode onto Rashford’s pass to fire home his first United goal before Rashford got in on the act with seconds left as thumped home Fernandes’ through ball.
FULL TIME AT ST. JAMES’ PARK IT’S NEWCASTLE 1 MANCHESTER UNITED 4