The 6ft 6in German centre-back produced a composed display alongside captain Thomas Vermaelen as the Gunners battled to a 3-1 win at West Ham.
After being undone by a fine opening goal for midfielder Mohamed Diame, it was a test passed which Mertesacker believes shows Arsenal, with former defender Steve Bould now assistant manager, have the capability to close out crucial phases of games this season.
"It can be the difference, it is crucial for us that the defence is winning more than just games. We just try to keep that in our mind the whole year," he said.
"We have not conceded a lot of goals during games this year, most have been from set pieces.
"We just need to keep concentrating on our defensive level."
Mertesacker recovered from a virus to return to the heart of the defence, having been left on the bench for the 2-1 home defeat to Chelsea.
With Lauren Koscielny the other option for manager Arsene Wenger depending on what challenges the Gunners face - yesterday's was the aerial threat of fit-again England striker Andy Carroll - there seems to be little prospect of a regular defensive partnership.
Mertesacker, 28, sees that as a positive.
"The manager told us before the start of the season that we have a lot of good centre-backs and is convinced we can make the team stronger and stronger because we have a lot of these good players in every position," he said.
"The manager said he would change sometimes and I think that's great for our development."
Mertesacker added: "The dressing room is full of good lads, we are looking forward to every game.
"All of the subs who came in against West Ham were fantastic and we have a great squad, we can feel the confidence rising."
The form of midfielder Santi Cazorla has certainly helped rejuvenate the Gunners.
The industrious Spaniard, a summer signing from Malaga, cracked in a superb 25-yard left-foot effort to wrap up the 3-1 win with seven minutes left.
"Cazorla makes everybody a better player," said Wenger.
"When you see these kind of players don't play for Spain [regularly], it just goes to show how good they are.
"He is right footed, but when you watch him play you don't know.
"Glenn Hoddle was like that, left-footed, right-footed, you could not say what he was, Cazorla is on that front similar.
"I don't remember anyone else I have worked with who was as much two-footed as that."
Theo Walcott came off the bench to net a crucial second goal on the break with a well-taken finish.
The England forward has yet to agree a new deal, but Wenger is not overly concerned.
"We are always in touch," the Arsenal manager said.
"He has character, Theo. He keeps focused and he wants to show he is 100% professional and I have a big respect for that attitude."