The Frenchman scored the Gunners' third goal in their 5-2 victory at the Emirates in the Premier League.
"It's nice to have marked my territory in the North London derby," he told French radio station RTL.
"We needed to resume our progress up the table, especially since we recently lost points rather stupidly. It was the right time to have a great game.
"We were good and we responded well after conceding the first goal. For my part, individually speaking, I feel better and better in this team."
Arsenal are currently sixth in the league standings with 19 points from 12 matches.