LONDON - Chelsea went five points clear of reigning champions Manchester City at the top of the Premier League after a 2-0 win at home to Arsenal in a fiery all-London clash on Sunday.
Eden Hazard gave Chelsea a 27th-minute lead with a coolly-taken penalty after he had been brought down in the box by Gunners defender Laurent Koscielny.
Diego Costa's ninth goal in seven Premier League games after an excellent lofted through-ball from former Arsenal favourite Cesc Fabregas sealed Chelsea's victory 12 minutes from time.
Kick-off at Stamford Bridge was delayed by 15 minutes as officials slowed the entry of Arsenal fans into the away end after a flare was set off.
There was a flare-up of a different kind when Arsenal manager Arsene Wenger clashed with Jose Mourinho after the Gunners' Alexis Sanchez was fouled by Gary Cahill.
"There are two technical areas not one," said Mourinho. He (Wenger) was coming to my space." Chelsea goalkeeper Thibaut Courtois then went off due to suspected concussion following an earlier collision with Sanchez.
Wenger, whose side were thrashed 6-0 on their last visit to Stamford Bridge in March, did not to dwell on his clash with Mourinho but suggested Arsenal had been unluck.
"They did not work our keeper more than we did their's. We had more shots and missed opportunities to take more," he said.
The defeat, Arsenal's first in the Premier League this season, left the Gunners nine points off top spot and meant Wenger had failed to beat a Chelsea side managed by Mourinho in 12 attempts.
Earlier, Radamel Falcao's first goal for Manchester United secured a 2-1 victory over Everton.
Colombia striker Falcao - signed on loan for a reported 10 million euros (S$16 million) on transfer deadline day - marked his fourth United appearance by scoring from inside the box after getting on the end of Angel di Maria's long-range shot in the 62nd minute.
Argentina midfielder di Maria had given United a 27th-minute lead when he curled in a shot from just inside the penalty area after an excellent pass from Juan Mata.
Everton could have equalised on the stroke of half-time following a penalty awarded when Luke Shaw brought down Tony Hibbert but United goalkeeper David de Gea saved Leighton Baines's spot-kick - the first of several fine stops.
However, Baines recovered his composure to whip in a superb cross from which Gary Naismith headed Everton level 10 minutes after the break.
Stoppage-time saw de Gea preserve United's lead with two impressive saves to deny Everton substitutes Leon Osman and Bryan Oviedo.
The result meant United had their first back-to-back successes under Dutch manager Louis van Gaal following last week's 2-1 victory at home to West Ham.
'Fantastic de Gea'
"David de Gea was fantastic," van Gaal told the BBC before saying of his new goalscorer: "Falcao was forcing himself last week against West Ham. I told him to be satisfied about his performances and that the goals are coming. The goals are coming!" Everton's defeat was compounded by John Stones being carried off on a stretcher late on - with the defender's now set to miss England's Euro 2016 qualifiers against San Marino and Estonia next week.
"John Stones has an ankle ligament problem. It's too early to know the extent of it but it must be something serious for him to come off," said Everton manager Roberto Martinez.
Christian Eriksen's 40th-minute shot from the edge of the box was good enough to give Tottenham Hotspur a 1-0 win at home to high-flyers Southampton - the club Spurs manager Mauricio Pochettino left before moving to White Hart Lane in pre-season.
"We are still improving," said Pochettino after overseeing Spurs' third victory in seven league matches this season.
"I arrived three months ago. It is always difficult to put together a different philosophy in such a short time." The Argentinian added: "I love Southampton and the club. Southampton will always be special for me in my heart." Meanwhile QPR manager Harry Redknapp and goalkeeper Robert Green both returned to West Ham in Sunday's second all-London clash.