Mertesacker admits that it was important for the side to get back to winning ways after losing to Dortmund in the Champions League in midweek.
"We wanted to come back as quickly as possible as a strong unit," he told the club's official website. "What we showed was good enough to respond, but there will be more tests to come and that will be crucial for the rest of the season.
"We want to surprise people more and more, that is what we need to do but we do not look too much at the other sides. We are in a strong and interesting position, so we are aware of it and try to keep it - but that is the difficult thing, to keep it."
Arsenal return to action on Tuesday night when they host Chelsea in the fourth round of the League Cup.