Ten-man Newcastle inflicted Michael Carrick's first defeat as Manchester United boss as substitute William Osula's superb 90th-minute strike sealed a 2-1 win.
Eddie Howe's side overcame the adversity of Jacob Ramsey's controversial first-half sending off, awarded after an apparent dive under a challenge from visiting goalkeeper Senne Lammens, to end a run of three consecutive home league defeats.
In a chaotic first-half stoppage-time, kicked off by Ramsey's second yellow, Anthony Gordon put Newcastle in front from the spot after winning a penalty from Bruno Fernandes but United quickly equalised as the skipper made amends by setting up Casemiro.
It looked like Manchester United would benefit from their opponents having a player sent off for the second game running, however it was Newcastle that posed more danger in a dire second-half from Carrick's side that does not come entirely as a surprise.
This is only Carrick's first setback, but the past three games had exposed frailties that were laid bare at Newcastle. Doubts, inevitably, will creep in. It might not help Carrick that the loss came against Howe,
Newcastle required a few top saves from Aaron Ramsdale, chosen ahead of Nick Pope, to stay in the game before Osula, who has barely played this season, became the first substitute to score a 90th-minute winner against Manchester United in the Premier League.
Manchester United stay third despite their first loss under Carrick, a winner in six of his first seven games, after Champions League-qualification rivals Aston Villa, thrashed 4-1 by Chelsea, suffered back-to-back defeats. Newcastle, meanwhile, are up to 12th.
Man Utd boss Michael Carrick speaking to TNT Sports:
"We're not happy with the way we played tonight. We had it in our hands largely but credit to Newcastle.
"The way they approached the game, we knew it would be a tough game. We navigated the game in a way that we felt we could kick on but we didn't really. Bitterly disappointed.
"I don't think it was the 10 men, I just don't think we played good enough tonight. We can't make any excuses for that. We all take responsibility for that and we know.
"Why was the character lacking? It wasn't. It was just the quality and the performance. Not the character. We wanted to win. It's easy to throw that out when you don't win a game of football.
"We weren't there in terms of quality. Credit to Newcastle. They deserved to win tonight. It hurts me to say that but that's how it was. We need to get back to working and be better for the next game.
"We've lost one game, we haven't played well enough but in the grand scheme of things but we are in a good position."
Newcastle boss Eddie Howe to TNT Sports:
"We did really well in the first half. We were quite fluid with the ball, we were back to combining and playing as a team, playing in partnerships.
"I was really pleased apart from the last bit. I felt we deserved the goal lead at half-time. Then they scored from a free kick that I personally didn't think was a free kick either.
"It was one of those days where it would have been very easy for the players at half-time to feel sorry for themselves, especially after the recent run we've been on.
"There was real collective mental strength to regroup and produce the second half that we did."
Newcastle's match-winner Will Osula speaking to TNT Sports:
"That was, like, the best feeling ever. I was so happy for that. You know, when I came on, I just prayed I was going to score, make something happen, and thank God that happened.
"I was practising that in the finish yesterday in training. Any chance, cut in and finish it. So I'm happy the hard work paid off."
Clinton Morrison on Soccer Special:
"Newcastle did it because they have a brilliant manager. Eddie Howe. When Thomas Tuchel moves on, he will be the England manager.
"The players run through brick walls for their manager. Tonight, they were outstanding.
"When the pressure is on, you look at if the players are still playing for their manager. They are 100 per cent still playing for their manager.
"Man Utd were nowhere near good enough."
