Arsene Wenger's side, who had won their opening four matches of the season comfortably - netting 15 goals in the process - appeared set to seal a surprise win at the Theatre of Dreams courtesy of Arshavin's first-half thunderbolt.
But the Red Devils, who had barely mounted an attack on goal beforehand, were then handed all three points on a plate after Manuel Almunia needlessly upended Wayne Rooney inside the penalty-area - with the striker converting from the spot - before Abou Diaby headed Ryan Giggs' harmless set-piece into his own net.
And Arshavin, who hobbled off injured during the latter stages of the clash and is now out of Russia's meeting with Liechenstein this weekend, believes the Gunners were too defensive once they had taken the lead, and should instead have continued pressing for a crucial second goal.
“I am upset with the result,” he said.
“Yes, we suffered a first defeat, which, I think, should just give us additional strength. We will draw our conclusions from how this happened.
"Why did we lose? Once we scored, the team should not have retreated into our half, but instead should have continued to play our brand of game - to attack the goals of the opponent, rather than play to retain the lead.
"In the second half Manchester pressured us a little and this ‘little’ was enough to score two goals against us. After that we started playing again, but it was already not enough. Three points lost.”
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