Liverpool’s flawless Premier League run ended with a 2-1 loss at Crystal Palace on Saturday, while Manchester United stumbled again in a 3-1 defeat at Brentford.
Palace are now the only undefeated team in the Premier League after extending their club record run to 18 games in all competitions without losing, including three games against Liverpool.
"These are the moments why we love football. The fans will have a great Saturday evening now," said Palace boss Oliver Glasner.
"We deserved it. Great performance, great game, great win."
The English champions were finally made to pay for another disjointed performance after being bailed out by a series of late goals in winning their opening five league games.
Ismaila Sarr fired the FA Cup winners into an early lead after Liverpool failed to deal with a corner.
Liverpool looked set to be rescued by another late goal when Federico Chiesa swept home a loose ball in the box to equalize in the 87th minute.
This time, the Reds were on the other end of a late winner.
Nketiah produced a composed finish in a packed penalty area with almost the last kick of the game.
Victory takes Palace up to second and within three points of Liverpool at the top of the table.
Arsenal can move back into second and cut the gap on their title rivals to two points when they travel to Newcastle on Sunday.
United boss Ruben Amorim's wait for back-to-back Premier League wins goes on, nearly a year into his reign, after a disastrous defensive display at Brentford.
Igor Thiago took advantage of mistakes from Harry Maguire and goalkeeper Altay Bayındır to put Brentford 2-0 up inside 20 minutes.
Benjamin Sesko's first United goal was the only positive note for Amorim's men as the Slovenian fired in at the third attempt before halftime.
The course of the game could have been very different had Bruno Fernandes not failed to score from the penalty spot for the second time already this season.
Fernandes' spot-kick was saved by Caoimhin Kelleher after Nathan Collins was lucky to avoid a red card for pulling down Bryan Mbeumo.
Instead, it was Brentford who sealed victory in stoppage time through Mathias Jensen, whose shot proved too powerful for Bayindir.
"We didn't control the game. We played the game of Brentford," Amorim said.
"All the crucial moments were against us. We need to do better."
Manchester City needed some help from Burnley defender Maxime Esteve, who scored two own goals, in a 5-1 win for Pep Guardiola's men.
Esteve turned into his own net under pressure from Phil Foden after Jeremy Doku's effort was saved.
Against the run of play, Burnley hit back through Jadon Anthony to level before halftime.
City were growing frustrated until Matheus Nunes blasted in from Erling Haaland's knockdown.
The unfortunate Esteve turned in Nunes' cross to make it 3-1.
Haaland then struck twice in added time to take his tally for the season to 15 goals in nine games for club and country.
For the second consecutive weekend, Chelsea were undone by a red card in a 3-1 defeat to Brighton.
The Blues deservedly led at half-time through Enzo Fernandez's header.
However, the game changed when Trevoh Chalobah was sent off on 53 minutes after a VAR review for chopping down Diego Gomez, who was racing clear on goal.
Brighton made the man advantage count as Danny Welbeck headed in to level before Maxim De Cuyper and Welbeck secured victory in stoppage time.
Tottenham needed a 94th-minute equaliser from Joao Palhinha to rescue a 1-1 draw at home to bottom-of-the-table Wolves.
Newly-promoted Sunderland are up to fourth after Omar Alderete scored the only goal at the City Ground to leave Ange Postecoglou still without a win as Nottingham Forest manager.
There was also late drama at Elland Road, where Bournemouth snatched a point against Leeds thanks to Eli Kroupi's strike in a 2-2 draw.
