The defender says Arsene Wenger told them to focus on going at the game with full intensity, which they executed perfectly.
The victory has put the Gunners firmly back in the title race once again, and Mertesacker says the standards on show against the Red Devils must be maintained, with consistency now a key factor.
“We need to focus on ourselves and manage to do that in the first 20 minutes like we did against Manchester United and defend the way did together as a unit,” he told arsenal.com.
“We need to have a certain consistency [in the league] otherwise it is going to be difficult. But, if you get wins against the good teams then it will breed confidence for the whole team and we look forward to the next few Premier League games now.”
The defender says that the key to victory over United was giving everything as a collective from the start, without any hesitation.
They were keen to put things right against Louis van Gaal’s side after suffering a disappointing defeat against Olympiakos in the Champions League, with their hopes of progressing in that competition left hanging by a thread.
Arsene Wenger had to motivate his side with scrutiny firmly upon them, and Mertesacker says that the side were told to go at full intensity and focus on playing with tempo and speed, something they did to great effect.
“It worked completely because we gave everything from the start without any hesitation,” he added.
“[We were told to] do what we are best at and to go at full intensity, especially at home. Have no regrets and to focus on our job which is to have good possession in the final third, and play with tempo and speed.”