The North London outfit led until the 65th minute, but Gallas is adamant that his side must do better when in possession of the ball.
"I think we can play better," Gallas said. "We didn't keep the ball very well and that was key to the game.
"We tried to defend very well but City pushed up a lot and changed their tactics. They played with three at the back and started to push us but we were very frustrated because we didn't have the occasion to score a second goal."
Spurs travel to Arsenal in the North London derby next Saturday.