The Premier League title challengers were eliminated by defending champions Bayern at the same stage of last year's competition, losing on away goals after a 2-0 win at the Allianz Arena had brought the tie level at 3-3 on aggregate.
Arsene Wenger's men have the chance to avenge that defeat and will look to take control of the tie when they welcome Bayern to the Emirates Stadium on Tuesday.
But Germany international Mertesacker knows that Arsenal will need to produce a pair of faultless performances if they are to overcome Pep Guardiola's side - who have lost just one game in all competitions this season - and keep their hopes of a maiden Champions League triumph alive.
"We have to go for two perfect games against them (Bayern)," Mertesacker said. "We know we can beat them now, so maybe mentally we are in a better condition that last year.
"We respected them too much in the first leg then, so it was too easy for them.
"Maybe we have learned something from those lessons and will do better this time.
"Now we have another chance - and an opportunity to beat the champions. We want to achieve something exceptional this season, so we have to beat the best.
"That is not only Manchester City and Chelsea (in the Premier League). That is Bayern Munich in the Champions League."
