Arsenal beat Chelsea 3-0 after first half blitz

* Sanchez scores the opener after back-pass mistake by Cahill

* Walcott makes it 2-0 as Arsenal open up fragile Chelsea defence

* Ozil volleys in third on the break after exchange with Sanchez

* Arsenal's first league win against Chelsea in 10 attempts

* Arsenal next league game is at Burnley, Chelsea visit Hull ARSENAL 3 CHELSEA 0 Sept 24 (Reuters) - Arsenal cruised to a 3-0 win over Chelsea on Saturday, scoring all three goals in the first half to claim their first Premier League victory over their London rivals in 10 attempts.

Arsenal gave their manager Arsene Wenger something to celebrate as he marked 20 years in charge of the club, punishing Chelsea for poor defending to race into a 2-0 lead within 15 minutes.

First, Alexis Sanchez pounced on a feeble attempt at a back pass by Chelsea defender Gary Cahill to beat the advancing Thibaut Courtois with a neat chip in the 11th minute.

Three minutes later, Arsenal were 2-0 up as Hector Bellerin found himself in space on the right and picked out Theo Walcott who blasted home from close range.

Chelsea's attempts to claw their way back were effectively finished in the 40th minute when Mesut Ozil picked up a loose ball deep in the Arsenal half and raced forward to exchange passes with Sanchez and volley the hosts into a 3-0 lead.