The Frenchman was convinced the Spanish midfielder should not have been shown a red card, but was pleased to see his side dig in to secure three points against Crystal Palace
The Spaniard, who had netted from the spot moments earlier, hauled down Marouane Chamakh on the halfway line and was adjudged to have denied the Moroccan a clear goalscoring opportunity, and will now miss the Capital One Cup tie against Chelsea.
But Wenger has disputed the decision, claiming other players were covering for the Spaniard, though was pleased by his side's resilience after being reduced to 10 men.
“I honestly believe it was the wrong decision,” Wenger told BT Sport afterwards.
“Why? Because it has to be a clear goalscoring opportunity - it was very far from goal, he was not the last man. Even the foul was accidental. I think he got that wrong.
“We've shown a lot of resilience and patience and good organisation against a team who was really up for it. When we went down to 10 men we mastered the situation quite well.”
Olivier Giroud, who netted late on to wrap up the win, shared his manager's bemusement with the sending off, but lauded the manner in which his team-mates rallied despite their inferior numbers.
“I think it's quite a tough decision,” said the France international. “I think we have another defender who came back in front of Mikel, so it's quite a hard decision to take.
“But after we deserved our win because we never gave up and showed lots of courage and togetherness.”