5 things we learned from the Premier League this weekend

Manchester City assumed the Premier League lead on goal difference after Liverpool's 100 per cent start was ended at Chelsea. All three are unbeaten, while Manchester United are floundering.

Here, Press Association Sport looks at these and other talking points from the weekend's action in the Premier League.

Mourinho's bubble burst?

West Ham on Saturday inflicted Manchester United's third loss in seven games for the Red Devils' worst start since 1989-90, piling further pressure on boss Jose Mourinho. Former United players Rio Ferdinand and Paul Scholes have warned of further deterioration. Ferdinand told BT Sport: "You can't let a situation like this continue throughout the season – wars in the press, leaks, players on one side of the dressing room, Mourinho and his staff on the other. If that continues this will be one of the worst seasons in the club's history." Games with Valencia and Newcastle before the international break could be crucial for Mourinho's future.

Can Chelsea sustain title challenge?

While Mourinho is embattled and United are reeling, his former club Chelsea are apparently revived under Maurizio Sarri, a 59-year-old former banker. The enjoyment is back at Stamford Bridge and the Blues ended Liverpool's 100 per cent start on Saturday – and were within a few minutes of inflicting the Reds' first loss. Sarri says Chelsea are closer to Liverpool and holders Manchester City than he thought, but still maintained a top-four finish must be the objective, playing down his side's title prospects.

Gunners growing under Unai

Monday marks 22 years since Arsene Wenger took charge at Arsenal and the Frenchman's former team appear resurgent under his successor Unai Emery. The Gunners have now won seven successive games – five of them in the league – under the Basque, who succeeded Wenger in the summer. There will continue to be teething problems in the transition, but the signs are now promising after Saturday's 2-0 win over Watford.

Clear candidates for relegation battle

Newcastle, Cardiff and Huddersfield remain without a win this season. Fulham, Southampton and Brighton have just one each. There already appears to be a gap at the bottom. West Ham have proved a few wins can result in an elevation up the table, while Wolves' strong start shows not all newly-promoted clubs need to be in trouble. For those bottom seven, they need to string together positive results swiftly.

Silva lining?

Everton's urgency to muscle their way into the Premier League's elite has been underscored in recent years by a series of rash managerial appointments. After four games without a win, some were even beginning to grumble about Goodison's current incumbent, Marco Silva. But his side's second-half performance against Fulham suggested Silva and Everton could belatedly be on the right track towards attaining the kind of status they understandably crave.