Manchester United were full of confidence on Tyneside but made to wait for goals as a strong defensive performance from Newcastle United denied them for over an hour.
Martin Dubravka's error allowed Romelu Lukaku to open the scoring for Manchester United with his first touch, seconds after being introduced just after the hour mark.
On the 80th minute, Marcus Rashford - who was lively throughout - doubled their lead on the counter-attack.
Newcastle had shown a couple of bright moments going forward but Christian Atsu and Soloman Rondon, who each had chances to score, were unable to provide a finishing touch.
After 21 Premier League games, this was just Manchester United's third clean sheet and the first under Ole Gunnar Solskjaer as they closed the gap on the top four to six points. It was 11 when the Norwegian took over, just over a fortnight ago.
This was Newcastle's eighth home loss already this season, as Rafael Benitez is left firefighting for the second half of the season once again. They're now just two points above the relegation zone.
Solskjaer shows another way to win
Cynics might question the sea change under Solskjaer given the quality of opposition faced so far, but Jose Mourinho has famously never won a league match at St. James Park and Manchester United suffered a 1-0 defeat here last season.
Without an early breakthrough, and against a well-drilled Newcastle defence, Manchester United had to work harder than the first three matches under Solskjaer's short reign so far.
As such, this was more illustrative of their potential with the interim coach in charge than the processions of his first three matches, each of which were practically won by half-time.
In spite of their long wait for an opening, they demonstrated the same proactive, front-foot approach that’s defined their early days following Jose Mourinho’s sacking. In the first half, they enjoyed 72% possession, constantly playing through balls to willing runner Rashford.
With large swathes played in the final third, imagination and incisive passing, this is no longer a team that looks content to bide time and pounce on opposition mistakes.
Ironically, it was to be an opposition mistake that allowed Solskjaer's team to go ahead as Lukaku was allowed to tap in Dubravka's spillage, which was forced by Rashford's fierce dipping free-kick.
They confirmed the result on 80 minutes as Rashford was left with time and space to put the finishing touch on an incisive counter-attacking. Solskjaer's other attacking substitute, Alexis Sanchez - who has missed the last nine matches with a hamstring injury - played the ball across to him for the assist.
Paul Pogba might have made it three as he took the ball past Dubravka in injury-time, but hit the side netting from his wide angle.
An uncharacteristic error from Martin Dubravka leaves Newcastle frustrated
Jamaal Lascelles, who has rarely captured his best form of the last campaign, put in an authoritative and commanding performance to deny a lively, confident attack that featured Anthony Martial and Rashford allowed to run and show their creativity throughout the first half.
Overall it was a strong defensive performance that was only undone by a goalkeeping error, uncharacteristic from Dubravka after he followed his man of the match performance in this fixture last February with a solid and reliable first year at the club.
Newcastle did well to withstand the first-half pressure, as Atsu was lively as he looked to drive at the opposition on the counter. Rafael Benitez looked to add more impetus early in the second half as he introduced Jonjo Shelvey for an injured Mohamed Diame.
Shelvey, who was at fault for Watford's equaliser as he switched off to allow Abdoulaye Doucouré to head in unmarked, gave away possession in a dangerous area in his first act as second-half substitute.
But otherwise in possession, he made an instant impact, showing his eye for a through ball is unmatched in Newcastle's midfield and his ability to shoot from distance gave Manchester United's backline something new to worry about.
They couldn't make the breakthrough though, as Phil Jones - who had a customary shaky moment early on and was filled with nervous energy - grew into the game and kept Newcastle's clear-cut chances to a minimum.
Takeaways
Christian Atsu can provide the spark missed by Kenedy for Newcastle
It was last January that Kenedy arrived on loan from Chelsea and gave Newcastle's attack another dimension. It was seen as a coup to retain his services for this season, but the Brazilian has so rarely been at his best this season.
Atsu, who has rarely shown up in the Premier League, was Newcastle's most incisive and dangerous player on the night, demonstrating a guile that Kenedy has lacked in recent months. If he could have just provided a finishing touch it all might have been different.
Pogba and Shelvey not afraid to add spice
Pogba was marauding down on goal and looking to double Manchester United's lead when a raking challenge from Shelvey brought him down as replays showed he should have seen a red card.
The Frenchman did not forget and made sure he had his revenge with a late challenge to take down the Newcastle man. Both men are unafraid to stick the boot in, something which has proved costly for each of them in the past.
Man Of The Match - Marcus Rashford
Once again, this looks like the bright young striker that plays with fearlessness for England. Despite a series of robust challenges, he shook off his recent knock to put in a lively performance. Constantly running at the defence, he eventually made the telling contributions. His fizzing free-kick caused the first and he showed composure to finish the second.