Arsenal suffered their first Premier League defeat since April as William Saliba's red card triggered a shock 2-0 loss at Bournemouth on Saturday, while Manchester United eased the pressure on Erik ten Hag as they fought back to beat Brentford 2-1.
Mikel Arteta's side had started the campaign with a 10-match unbeaten run in all competitions, but that streak was shattered in controversial circumstances on the south coast.
Arsenal defender Saliba was sent off after half-an-hour for a professional foul on Evanilson that was initially punished with a booking before being upgraded to a red card after a VAR review.
The Gunners finally cracked in the closing stages as Ryan Christie put Bournemouth ahead.
Justin Kluivert's penalty ensured Arsenal would lose for the first time in the league since their 2-0 defeat against Aston Villa in April.
It was a bitter blow for Arsenal, who would have gone top with a victory but now have to face title rivals Liverpool next weekend without the suspended Saliba.
Third-placed Arsenal will be four points behind Liverpool by then if the leaders defeat Chelsea at Anfield on Sunday.
"It's very difficult to win in the Premier League with 10 men for 60 minutes, it's just an accident waiting to happen," Arteta said.
"We have had to go through it in three games and that cost us the game."
United manager Ten Hag had defiantly slammed "fairy tales and lies" about his future at the club on Friday as the beleaguered boss insisted he was not in danger of the sack.
But the 54-year-old is widely believed to be fighting to save his job after presiding over United's worst start to a top-flight season since 1989-90.
Ten Hag was surely teetering on the brink of being dismissed after Brentford pounced to take the lead in first-half stoppage time when Ethan Pinnock met a corner with a powerful header.
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