London - Manchester United became the first of the Premier League's top five last season to falter in the new campaign as shoddy defending saw Jose Mourinho's men defeated 3-2 at Brighton on Sunday.
READ: Mourinho fumes as United crash
Ominously for United, their cross city rivals and defending champions look in no mood to be caught as Manchester City thrashed Huddersfield 6-1, while Chelsea and Tottenham Hotspur maintained their perfect starts.
Here, AFP Sports looks at five things we learned from the Premier League weekend.
No case for United's defence
Mourinho's pre-season predictions of doom if he wasn't given the funds to strengthen United's defence came true in a disastrous first 45 minutes for the visitors at Brighton.
Mourinho's priority was to bolster his central defence, but it was the two centre-backs signed under his tenure for a combined £60 million, Victor Lindelof and Eric Bailly, who were at fault.
Lindelof left Glenn Murray unmarked for Brighton's opener, while Bailly chopped down Pascal Gross to concede a needless penalty just as United had got back into the game thanks to Romelu Lukaku's header.
"We made incredible mistakes in some crucial moments. Mistakes that killed us," said Mourinho.
Chelsea's new commander in chief
Based on the Italian international's start to life in England, had City beaten Chelsea to the signature of Jorginho, the champions would be even more of a terrifying prospect.
Instead, Jorginho has been charged with helping Maurizio Sarri impose his fine balance of possession and pressing that characterised their time together at Napoli.
The midfielder dictated the tempo of a thrilling opening period from the blues in Saturday's 3-2 win over Arsenal.
As he wilted so did his side as the Gunners roared back from 2-0 down to level just before half-time in a 15-minute spell which the chain-smoking Sarri said left him in need of a cigarette.
The break came at the right time for Chelsea as Jorginho regained control in the second period to help maintain a perfect start for Sarri.
Spurs' World Cup stars still standing
Pep Guardiola suggested World Cup fatigue may have played a role in a knee injury for Kevin de Bruyne that will keep the Belgian sidelined for three months, but Tottenham's World Cup contingent have hit the ground running despite barely a week of pre-season training.
Spurs' players logged more minutes in Russia than any other Premier League club and while fatigue may yet undermine a title challenge, they have put their off-field troubles in the transfer market and delays in the completion of their new stadium to one side by beating Newcastle and Fulham.
Kieran Trippier repeated his World Cup heroics with a stunning free-kick and Harry Kane ended his August hoodoo to send Spurs in fine fettle for a huge clash at Manchester United next Monday.
Sealed with a kiss
Gone are the days when Pep Guardiola was happy to leave City's all-time top scorer Sergio Aguero on the bench.
The Argentine scored his ninth Premier League hat-trick in a 6-1 annihilation of Huddersfield.
Aguero's goalscoring ability was never in doubt, but it is an improvement in his all-round game under Guardiola that has won over the Catalan coach.
"He feels free now. He just doesn't score goals, he makes space and doesn't stop and when he does that, he's one of the best strikers in the world," said Guardiola.
No wonder he planted a kiss on Aguero's cheek when he came off to a standing ovation.
More woe for West Ham
A near £100 million investment in nine new players and a Premier League winning coach was meant to signal a change in fortunes for West Ham after a troubled couple of campaigns on and off the field.
Instead, there has been no immediate return on that investment as a 4-0 opening weekend thrashing at Liverpool was followed by a 2-1 home defeat to Bournemouth.
Jack Wilshere is one of the new arrivals who is so far yet to live up to expectations and admits West Ham need to find their feet quickly under Manuel Pellegrini before his return to Arsenal next weekend.
"We have got a lot of new players and we need to gel," he said. "At this level in this league, people aren't given time, so we have to do it quick and all tuck in this week."