The German defender says it was a tough evening for Robert Lewandowski as a result of their defensive display.
The Gunners ran out 2-0 winners against the in-form Germans at the Emirates on Tuesday night, a result that keeps their Champions League hopes alive after two disastrous losses in their first two games.
It was an impressive performance from the entire team against Pep Guardiola’s side, but in particular the defence and Petr Cech were in fine form to keep their opponents at bay for the 90 minutes.
And Mertesacker says their defensive solidity was an aspect that particularly stood out.
“Our defensive unity from the start and for 90 minutes, I think that stands out today,” he told arsenal.com.
“We had to keep our focus on our defensive unit and stay as strong as possible and keep [them from scoring] for as long as possible. That was the key tonight. We had good chances but our team play was outstanding today and that was the most important thing.”
Much of the focus before the game had been on how the Arsenal defence were going to stop striker Robert Lewandowski, with the Polish striker currently in red hot form for club and country.
They did just that though, as he was limited to few chances in the game, with his one big opportunity seeing him denied by a superb save from Petr Cech to keep the score at 0-0.
Mertesacker in particular had to focus on Lewandowski for much of the night, and says it was a difficult day for him in general.
“It was difficult for him, he always tried to come a bit deeper to get the ball and get into the holes,” he added.
“I think he had a great chance in the second half but we have a great goalkeeper for him. It was not easy for him but I think he will score some goals in this season and he’s in good form at the moment. I’m sure he will continue his run.”