The Gunners, 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 Andriy Arshavin's first-half thunderbolt.
But Sir Alex Ferguson's side, 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 Diaby headed Ryan Giggs' harmless set-piece into his own net.
And the Frenchman, who came close to atoning for his error moments later, only to scuff his shot wide, says he wants to forget about the incident as soon as possible and help Arsene Wenger's men get back to winning ways.
"I have to forget it. I made a silly mistake and it's difficult to explain what happened," he said in The Sun.
"The goalkeeper called out to me to leave the ball, but it's all my fault.
"Even when I look back at the images I ask myself what happened, and I tell myself that it's just not possible.
"I was so wound up and soon after I rushed my shot because I didn't apply myself properly."
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