Consequently, the Toffees move to within a single point of the North Londoners in the race for Champions League qualification, and Wenger admits that is a "massive worry" to lose in such a fashion.
"Was there a lack of fight? You could say that. It is a massive worry to lose a game like that," he told reporters at full time.
"We have to analyse it well and come back with a different attitude, with more personality and stronger challenges. We have to go back to basics."
Wenger's men face Wigan Athletic in the FA Cup semi final at Wembley next weekend, before resuming league commitments by hosting West Ham United at the Emirates Stadium.