Wenger said: "Wigan played well defensively. We needed something special and some patience to find an opening, and Gallas found it.
"He is a forgotten centre-forward because he knows where to be in the box and he can always turn up with a goal when you need it.
"Once again we found the resources to win the game. It is not the first time, so I do not feel it is a coincidence."
Wenger added: "It [three point gap] is good for us because it strengthens our belief that we can compete at the top and we need that.
"We have a strong December and every point we can be ahead at the moment can be very good for us."