Wayne Rooney earned and converted a penalty after 59 minutes before Abou Diaby headed through his own net four minutes later.
Andrei Arshavin had given the Gunners a 40th minute lead with a thunderbolt shot but Arsenal have only themselves to blame after gifting the defending champions both goals.
Arshavin, who had not scored in the Premier League since his four goals at Liverpool last season, broke the deadlock with a 25-yard screamer.
Only moments earlier the Russian was claiming a penalty after Darren Fletcher had made a sliding tackle on him but he took out his frustration in the best way possible with a rasping shot than Ben Foster got a hand to but could not prevent from nestling in the roof of the net.
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