Mertesacker reckons those three results left their title hopes in tatters before the end of March - but insists they will not let it happen again next season.
He said: "Everyone questioned our qualities and our football. How we came back as a team, that makes us stronger for the future.
"We have to learn quickly how to play and how to defend in the first 20-25 minutes. It was very similar in each game.
"The first 20 minutes we lost some balls in the middle of the park, and they got us on the break. That is something we have to look at next year."