Arsenal's Leandro Trossard capitalised on dreadful Manchester United defending to secure a 1-0 win on Sunday that saw his side provisionally overtake Manchester City atop the Premier League and guaranteed the title race will go down to the final day.
While Arsenal, who won for just the second time at Old Trafford in their last 17 visits, have 86 points with one game left of the tightest title race in years, holders City remain in the driving seat with 85 points and two matches to play.
City, who are aiming for an unprecedented fourth consecutive English top-flight title, can retake the lead when they play at Arsenal's London rivals Tottenham Hotspur on Tuesday.
Trossard scored in the 20th minute when Kai Havertz sauntered barely challenged into space on the right before sending the ball into the box for Trossard to tuck home.
Heads turned to check for an offside flag but Casemiro -- recently moved from midfield into United's injury-depleted back line -- had slowly moved out from the box and kept Havertz onside after goalkeeper Andre Onana launched the ball upfield.
United manager Erik ten Hag was left shaking his head in frustration.
The game swung from end to end over a final tense few minutes, with Onana leaping to push away shots from Arsenal substitute Gabriel Martinelli and Declan Rice.
United, who were hoping to bounce back after a woeful 4-0 loss at Crystal Palace on Monday, are eighth with two games left. They trail sixth-placed Newcastle by three points in their quest for a European berth next season, setting up a key showdown when the Magpies visit Old Trafford on Wednesday.
Trossard's goal was the 82nd Ten Hag's team have conceded this season in all competitions -- their most in a single campaign since 1970-71
United enjoyed plenty of the ball in the final third, and had 14 shots to Arsenal's 11, but struggled to create many quality chances.
Alejandro Garnacho was United's biggest threat, particularly in the second half. He launched one shot wide and sent another into the side netting before hanging his head in frustration.
The visiting fans, whose singing did not let up all evening, erupted at the final whistle after a game that was tighter than predicted. Not even the torrential downpour could dampen their celebration after the job done by Mikel Arteta's team.
Arsenal host Everton in their season finale, while City are at home to West Ham United.
