Half-time: Arsenal 0 Chelsea 1 – Blues well on top against 10-man Gunners

Diego Costa’s 22nd-minute goal put Chelsea ahead in the derby at the Emirates Stadium shortly after Arsenal captain Per Mertesacker was sent off for a foul on the Blues striker.

The Gunners were reduced to 10 men following a Chelsea counter-attack led by Willian, who cleverly aimed a pass in behind Mertesacker for Costa, who would have been through on goal had the defender not brought him down.

Mertesacker was duly shown the red card by referee Mark Clattenburg, and the home fans reacted angrily to Arsenal boss Arsene Wenger’s reaction to the sending-off, which was to send defender Gabriel on in place of forward Olivier Giroud.

Seconds later, Costa drifted away from Gabriel to nudge home Branislav Ivanovic’s right-wing cross – his sixth goal in as many games.

Arsenal keeper Petr Cech, playing against his former club, had earlier denied Willian at point-blank range and pushed away a shot from Oscar.

Having found themselves a goal and a man down, Arsenal struggled to create chances.

Cech prevented them falling further behind three minutes before the interval when he kept out an effort from Costa at the near post, and Ivanovic’s header from the resulting corner was cleared off the line.

Then, in the final seconds of the half, Mathieu Flamini missed a great chance to equalise when he hurriedly hooked the ball over after being found unmarked inside the box by Aaron Ramsey.

Chelsea: Courtois; Ivanovic, Zouma, Terry, Azpilicueta; Mikel, Matic; Willian, Fabregas, Oscar; Costa.
Subs: Begovic, Cahill, Baba Rahman, Loftus-Cheek, Traore, Hazard, Remy.