But United took the game away from their lowly opposition after the break as Dan James continued his fine run of form with a goal and Bruno Fernandes converted a penalty.
The result leaves Ole Gunnar Solskjaer's side in second place, still ten points behind Manchester City, while Newcastle are 17th and now just three points above Fulham.
Here are five things we learned:
Europa League hangover
A recurring theme of United's season has been an inability to start strongly, often falling behind early on and almost using that as a catalyst to find some rhythm.
They didn't go a goal down here, but there was a shakiness, a nervousness about the hosts. It felt, too, like United might have been suffering from their trip to Turin to play Real Sociedad in the Europa League on Thursday night.
That competition has often been used as a convenient excuse, though there's no doubt that an extra midweek fixture at this point of the season can be draining. Solskjaer's side were sluggish in the first half, unable to play with the kind of tempo that helped them brush Real Sociedad away just a few days ago.
Fulham resurgence gives Newcastle some urgency
Not so long ago, Newcastle would almost certainly have approached this game entirely differently. They would have arrived at Old Trafford intent on defending, reluctant to commit and players forward and set in a rigid low block. And they would probably have lost anyway.
Now, though, things have changed. Bruce has listened to his many critics, setting up his team to be more proactive, to play on the front foot, even away at Old Trafford. That's what they did, keeping Harry Maguire and Victor Lindelof busy and often looking like the more creative of the two teams.
The reason for this urgency is obvious: Fulham, with their win over Sheffield United on Saturday, are closing in on Newcastle, who can no longer afford to coast through the season and assume enough points will be accumulated. They need wins, and more performances like this, even if they did fade in the second half, will help in that regard.
Midfield issues for United
United never really looked in control of this game, and that was largely because of a lack of any authority or precision in midfield.
Nemanja Matic and Fred were repeatedly guilty of playing wayward passes, gifting the ball to their opposition and ensuring that United couldn't build any attacking momentum.
With Scott McTominay and Paul Pogba absent, that becomes a problem area of the pitch for Solskjaer. It also means United are far too reliant on Bruno Fernandes to create chances. When he has a quiet day, as he did against Newcastle, there is very little guile elsewhere in the team.
Against better opposition, these issues could be more readily exposed.
Almiron and Saint-Maximin the key for Newcastle
There were concerns that Newcastle might become impotent without Callum Wilson leading the line. That's certainly not been ruled out, though the performances of Saint-Maximin and Miguel Almiron offered some hope.
The former took his goal well, guiding a half-volley into the ground and past David de Gea. And the latter was a constant menace, particularly in the first half, running at United's back four and getting into some dangerous positions.
Both players will have a big part to play if Newcastle are to pull away from the bottom three. But the question of who will regularly score goals in Wilson's absence remains.
James takes his chance
Few will begrudge James a good run in this United team. The young winger hasn't always thrived at Old Trafford, often on the fringes under Solskjaer and regularly criticised when he does feature.
Now, though, he is enjoying his best spell in a United shirt, scoring in each of his last three games, including a well-taken shot at the near post to put the hosts 2-1 up against Newcastle.
There is more work for James to do, of course. Mason Greenwood will hope to take his position on the right flank in the long term, and Solskjaer is certainly not short of options.
But the Welshman has given his manager something to think about over the last couple of weeks.
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