LONDON (AP) For a day at least, everything went Chelsea's way again in the Premier League.

After an unconvincing start to its title defense, Chelsea was given a double boost by beating London rival Arsenal 2-0 in a contentious game Saturday and then seeing leader Manchester City's perfect start end with a 2-1 home loss to West Ham.

Chelsea's day might have turned out less positively had Diego Costa not stayed on the field after swiping at Laurent Koscielny's face and then chesting the defender to the ground. Instead, it was Arsenal defender Gabriel Paulista who was sent off when he retaliated by kicking out at Costa after the two scuffled just before halftime - leaving Arsenal manager Arsene Wenger furious.

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''He will do the same next week and the week after and he always gets away with it,'' Wenger said about Costa. ''It's always provocation and he uses well the naivety of (referee) Mike Dean.''

The verdict from Chelsea manager Jose Mourinho on Costa was more succinct: ''Fantastic, Diego. ... Man of the match.''

Chelsea's opener came eight minutes after the break through Kurt Zouma's header, and any hope of an Arsenal comeback appeared to be evaporate in the 79th minute when Santi Cazorla was dismissed for a late sliding tackle on Cesc Fabregas.

Eden Hazard completed only the second victory of Chelsea's six-game old title defense in stoppage time with a deflected shot.

Mourinho maintained his unbeaten record against Wenger in a 14th competitive game and Chelsea finally started climbing up the fledgling Premier League.

The surprise sight near the top is West Ham in second place after stunning City, the 2012 and 2014 champions. City has 15 points with West Ham and fellow surprise package Leicester on 12.

Victor Moses put West Ham ahead after just six minutes with a low shot from distance, the first league goal City had conceded all season. Diafra Sakho doubled the lead in the 31st after a goalmouth scramble from a corner.

New signing Kevin De Bruyne pulled a goal back for City on the stroke of halftime from 20 yards, but West Ham held on despite sustained pressure from the hosts in the second half.

''I think we played too fast in the second half, too rushed,'' City manager Manuel Pellegrini said. ''You must be more calm but when you are two goals down, it is difficult. We had a lot of chances to score.''

It took a second-half fightback at Stoke for Leicester to stay unbeaten, with Riyad Mahrez's penalty and Jamie Vardy's strike recovering a 2-2 draw.

''It's unbelievable for the fourth time in a row we come back (after conceding),'' manager Claudio Ranieri said.

It left Stoke winless like Newcastle and Sunderland, with the north-east strugglers both losing to newcomers to stay on two points.

Callum Wilson and Matt Ritchie scored in the opening nine minutes to give Bournemouth a 2-0 win over Sunderland. Watford won 2-1 at Newcastle with Odion Ighalo taking advantage of poor defending to score twice in the opening 28 minutes.

''No one said this job was going to be easy and we didn't think it would be,'' Newcastle manager Steve McClaren said. ''It's a tough job ... it's very difficult to turn things round in two and a half months.''

At Villa Park, Saido Berahino scored his first goal for West Bromwich Albion since threatening to go on strike after a failed move to Tottenham as his team beat city rival Aston Villa 1-0.

There was only one goalless game on Saturday, with Everton striker Romelu Lukaku wasting a number of chances at Swansea.