Chelsea 2-0 Arsenal

Chelsea striker Diego Costa has now scored nine goals in seven Premier League games

• Chelsea five points clear at the top

• Costa scores ninth goal in seven league games

• Wenger not beaten Mourinho in 12 attempts

• Eden Hazard scores second goal of the season

Chelsea cemented their position at the top of the Premier League with victory over Arsenal as Arsene Wenger's winless streak against Jose Mourinho was extended to 12 games.

The old adversaries squared up in an ugly first-half moment when Wenger shoved Mourinho in the chest in Chelsea's technical area after Gary Cahill's challenge on Arsenal forward Alexis Sanchez.

A semblance of order was restored although the tension still resurfaced - but as so often, it was Mourinho who had the last word with a win that puts the Blues five points ahead of second-placed Manchester City.

Eden Hazard's first-half penalty put them on their way after he was fouled by Laurent Koscielny, while Diego Costa's ninth goal in seven games since his £32m summer move from Atletico Madrid wrapped up the win.

This never threatened to be a repeat of Chelsea's 6-0 thrashing of Arsenal in March that marred Wenger's 1,000th match in charge of the Gunners, but there was rarely a moment when his side threatened to end his dismal sequence against Mourinho as they suffered their first league loss of the season.

The home side may not have produced the flamboyant football that has featured in some of their play this season, but the old steel at the back is still in evidence and, in Costa and former Arsenal midfielder Cesc Fabregas, they have acquired a potent partnership.

Costa's goalscoring has caught the eye but the wonderful raking pass from Fabregas that set up the second goal silenced the taunts aimed from the visiting fans and was his seventh Premier League assist of the season.

It was the crowning moment of a Chelsea performance that was ruthlessly efficient and sounded an ominous note to those hoping to stop Mourinho reclaiming the Premier League title this season.

Fourth official Jon Moss had to step into a confrontation between Arsene Wenger and Jose Mourinho

Chelsea even survived the early loss of goalkeeper Thibaut Courtois, who was taken off before half-time and replaced by Petr Cech after taking a bang on the head in a collision with Sanchez, with the Belgian taken to hospital as a precaution.

Courtois's problems started when he raced out to beat Sanchez to a through ball and there was an accidental clash between the pair - the young goalkeeper recovered after being flat out but was unable to complete the half, the Chelsea medical team eventually signalling to Mourinho that he need to be replaced.

If the action on the pitch took time to get going, there was no time-wasting between Mourinho and Wenger as their obvious personal animosity quickly boiled over.

Wenger took exception to Mourinho giving his view on Cahill's tackle on Sanchez, marching menacingly into the Chelsea technical area before giving his counterpart a very clear two-handed shove in the chest.

Mourinho, not surprisingly, was unimpressed and it took the intervention of fourth official Jon Moss to at least restore a small measure of calm between the pair.

Arsenal had acquitted themselves well without putting Chelsea under serious pressure, but were unlocked by the pace and trickery of Hazard to go behind after 27 minutes. Koscielny had no other answer to the Belgian's run into the area than to stick his leg out and bring him down, with Hazard recovering his poise to score from the spot.

Chelsea, while not being at their best, had restricted Arsenal to the extent that the visiting attacking threat was non-existent, but the Gunners had a genuine grievance when Fabregas stopped Jack Wilshere's shot from the edge of the area with raised arms just after the hour, only for referee Martin Atkinson to remain unmoved.

And while Chelsea were resolute in defence, there remained the ever-present threat of Costa. He had barely been in the game but pounced to put the match out of Arsenal's reach with 12 minutes left.

Fabregas, as he has been so often this season since joining Chelsea from Barcelona in the summer, was the creator, as a long pass sent Costa beyond Arsenal's defence to lift a finish over Wojciech Szczesny.

Chelsea manager Jose Mourinho:

"The start of the season is good, but it's just seven matches and beginning of October.

"'I'm even more pleased to win because we played against a good Arsenal. They played a good game and gave us a difficult game.

"We were able to deal with it without problems, which is fantastic. When we were 1-0 up the game was almost in the pocket."

Arsenal manager Arsene Wenger:

"It was a very intense game and very tight as well.

"It was about not making a mistake and not giving the first goal away. After that we were 1-0 down.

"We had good opportunities in the first half and we have to turn these into dangerous situations and finish them.

"After that in the second half it was all us and we were a bit unlucky. We made a mistake on the second goal, and the second goal killed the game off."

Chelsea's Thibaut Courtois left the pitch with a head injury after a collision with Alexis Sanchez

Eden Hazard gave Chelsea the lead from the penalty spot with his second goal of the season.

Arsenal manager Arsene Wenger and Chelsea boss Jose Mourinho had to be separated after a spat

Chelsea striker Diego Costa is mobbed by his team-mates after scoring his side's second against Arsenal