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 red card, Anthony Gordon put Newcastle in front from the spot after winning a penalty from Bruno Fernandes' foul but United quickly equalised as the skipper made amends by setting up Casemiro's header.
Chaotic first-half stoppage-time broken down
45: Fourth official shows minimum of three additional minutes to be added on.
45+1: Ramsey sent off for second bookable offence for diving under a challenge from Lammens in the box.
Ex-referee Mike Dean said it was not a dive and Ramsey was "unlucky" to pick up another yellow.
45+5: Newcastle awarded penalty for a foul by Fernandes on Gordon.
45+6: Gordon scores from the spot to give 10-man Newcastle the lead.
45+9: Casemiro heads in Man Utd's equaliser from a Fernandes free-kick.
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 looked the more dangerous in a dire performance from Carrick's side that does not come entirely as a surprise.
United remain third despite losing their first game under Carrick, who won six of his first seven games in charge, after their Champions League rivals Aston Villa, thrashed 4-1 at home by Chelsea, suffered back-to-back defeats. Newcastle, meanwhile, are up to 12th.
More to follow...
Story of the match in stats
What's coming up in the Premier League?