The German was clearly shocked by the Gunners' defending in their 2-1 defeat in the north London derby and responded with clean sheets against Bayern Munich and Swansea City.
The Swans were not allowed a single shot on target by a defence that did not include captain Thomas Vermaelen.
"Sometimes as a player you have a different view and you can't believe what we did as a defensive unit," admitted Mertesacker. "Sometimes you need to learn from games and that was very important for us.
"There was a lot of room for improvement after the Tottenham game - we saw a lot of things on television. Sometimes we didn't choose the right direction and we just lacked a bit of defensive work as a unit.
"There were a lot of situations where there was no pressure on the ball and the back four was not prepared for any balls between us. To cover each other, that was the most important thing we learned."