5 things we learned from the Premier League this weekend

Liverpool maintained their flawless start to the season by sweeping aside Southampton, but Chelsea's 100 per cent record disappeared after they drew a blank at West Ham.

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

Liverpool on-song but tougher tests await

After dramatically edging out Paris St Germain in a heavyweight Champions League encounter in midweek, Liverpool could have been forgiven if they were not firing on all cylinders when Southampton came to Anfield. Saints would have been looking to induce a European hangover, but were thoroughly outclassed as the Reds ran out 3-0 winners, the game over as a contest before half-time. The definitive test to their title aspirations is approaching, though, with a trip to Chelsea next week followed by champions Manchester City travelling to Merseyside. In-between is a visit to Napoli in the Champions League. A tricky run, but if that does not derail them, then what would stop the juggernaut?

Chelsea fail to fire

The Blues have been going about their business in a rather understated way under new head coach Maurizio Sarri, but were matching Liverpool blow for blow until this weekend. West Ham took four points off the Blues last season and frustrated them again in a goalless draw on Sunday. Indeed, only the poor finishing of Michail Antonio and Andriy Yarmolenko spared Chelsea's blushes. It is their first setback under Sarri, but, with a resurgent Liverpool arriving at Stamford Bridge next week, they can ill-afford to lick their wounds. How they respond could define their season.

Mourinho questions United's attitude

Manchester United looked to have turned a corner after bouncing back from their humbling against Tottenham with wins at Burnley and Watford. But they delivered another disjointed display against Wolves and only some vital interventions from the formidable David de Gea spared them a second home defeat in succession as they settled for a 1-1 draw on Sir Alex Ferguson's emotional return to Old Trafford. Jose Mourinho, not for the first time this season, lamented his side's desire and believes they can learn a thing or two from Wolves' wholehearted approach, saying: "(Wolves) play like I like to play which is like the World Cup final. That's the attitude I like my teams to have every match. We didn't have that, they did."

Burnley are up and running

Sean Dyche admitted there was a "nervousness" at Burnley after four straight defeats and only one point from their opening five games, representing their worst start to a top-flight campaign for nearly a century. However, they ended their barren run in some style, cruising to a 4-0 victory over a Bournemouth side that sat in the top-five before this weekend's fixtures. It was a timely confidence boost as lowly Cardiff and Huddersfield are their next two opponents.

Cardiff need a win

Neil Warnock took a pragmatic view in light of Cardiff succumbing to their third successive defeat. The veteran manager was correct in his assessment that the 5-0 setback against Manchester City will not decide their top-flight fate. But they have failed to advance their cause this month – albeit following an undesirable run of fixtures against Arsenal, Chelsea and City – and next week's clash against Burnley is looking like a hugely important fixture.