Manchester City will enjoy a three-point Premier League lead for the next three weeks after Arsenal's perfect start came off the rails in a 3-0 defeat at Brighton.
City conceded three times themselves to Sunderland's Brian Brobbey but had enough firepower of their own to beat the Black Cats 5-3.
Chelsea were also defeated 3-0 at Brentford to take the shine off Xabi Alonso's start at Stamford Bridge, while Manchester United could only manage a 1-1 draw at winless Fulham.
AFP Sport looks at three talking points from the Premier League weekend:
The champions had been tipped to romp to the title after another summer of smart recruitment and a dominant start to the campaign.
But Brighton showed the rest of the Premier League that the Gunners do have flaws by inflicting their heaviest defeat in over three years.
Mikel Arteta's men arrived on the south-coast in formidable form having won all seven games in all competitions this season.
Arsenal, though, struggled to cope with the Seagulls' high press and were even uncharacteristically exposed defensively from a corner when Chema Andres headed in Brighton's third.
"The way we have competed, the way we have played, the way we have dominated. It's been really good," said Arteta on his side's start to the season.
"But today we need to take this lesson very, very seriously because it's going to happen."
Assailed by stinging criticism of Manchester United's abject performance in their 1-1 draw against lowly Fulham on Sunday, Michael Carrick mounted an unconvincing defence of his spluttering side as the pressure mounted.
United have won just once in five league games, equalling their worst start to the season in the Premier League era.
It would have been even worse for Carrick but for Matheus Cunha's last-gasp equaliser at Craven Cottage.
United trailed to a farcical second half goal that summed up their malaise as Lisandro Martinez made a hash of clearing from Senne Lammens's save and scuffed the ball into his own net via a deflection off his keeper.
Giving away possession carelessly time and again, while lacking the basic defensive solidity to contain a previously moribund Fulham attack, United looked no better than the lethargic group that struggled under Carrick's predecessor Ruben Amorim.
Carrick proved a stabilising force after replacing the sacked Amorim last season but the positives vibes created by that third-place finish are quickly fading.
Piling on the misery for Carrick, his former team-mate Gary Neville issued a damning indictment.
"I've watched Man United since the age of five and that's the worst 15 minutes I've ever seen," said Neville of United's start to the second half.
"Absolutely pathetic. I've never seen such a lack of effort. What must Carrick be thinking?"
The dazzling start made by Chelsea's front three of Joao Pedro, Cole Palmer and Morgan Rogers papered over the cracks of the Blues' defensive problems.
Chelsea have now gone three games without a win as their inability to keep a clean sheet goes on.
It is now 21 league games since they did not concede, the club's longest run since 1965.
That run predates Alonso's time in charge, but he knows a major change is needed after becoming only the sixth manager to concede at least twice in his first five Premier League games.
"Not good enough," said Chelsea defender Levi Colwill. "At times we have been bullied in the box and we definitely need to improve."
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