Mertesacker says that extra hours at London Colney were the key to Arsenal's defensive improvement.
"We had a little bit more time [during the week] because of the Carling Cup match," he told Arsenal Player.
"Some players had a little more rest and we trained a little harder, especially on the way we want to defend. It worked and on Saturday you saw we had a better defence. We were closer together.
"After the four goals against Blackburn we lost a little bit of confidence but we were very proud of our performance on Saturday. We want to go on with this way of defending.
"I want to do a good job, especially in the defence. That is my role. If the coach praises me then that is a great thing but I have to go on and keep on working. My performances can improve."