LONDON (AFP) - Chelsea went five points clear 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 on the touch-line, the Frenchman pushing his Portuguese counterpart to one side before the feuding bosses were separated.
Chelsea then saw goalkeeper Thibaut Courtois leave the field with suspected concussion following a collision with Arsenal's Alexis Sanchez.
Victory saw Chelsea go five points clear of second-placed reigning champions Manchester City and meant Wenger was still left searching for his first win against a Blues side managed by Mourinho in what was his 12th attempt.
This defeat, Arsenal's first in the Premier League this season, left the Gunners nine points off top spot.
It also extended their miserable away record at their English title rivals, with the Gunners now having won six points from 21 league matches at the home grounds of top five clubs.
Meanwhile, 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-flying Southampton - the club Spurs manager Mauricio Pochettino left before moving to White Hart Lane in pre-season.
QPR manager Harry Redknapp and goalkeeper Robert Green both returned to West Ham in Sunday's second all-London clash.