Two second half Robin van Persie strikes sunk the Blues, who suffered their second home defeat of the season, and had been leading thanks to an own goal Johan Djourou.
The Gunners scalp of the Premier League leaders means Liverpool can take full advantage and be outright leaders of the league with three points at Anfield tonight. It will be the first time the Reds have been top proper since beating Chelsea two months ago.
Other results yesterday saw Manchester United beat Manchester City at Eastlands, but had midfielder Christiano Ronaldo sent of for two yellow cards.
And former Red Peter Crouch was on target as Portsmouth survived a second half Blackburn Rovers comeback to beat Paul Ince’s team 3-2.
Liverpool vs West Ham kicks off at 8pm tonight.