Cech was heavily criticised for being at fault for both goals during the defeat.
"Petr is very experienced. You can feel that, he has lots of things to say and in the dressing room he gives us a great lift," Mertesacker, who made over 100 appearances for Germany, told the club's website (www.arsenal.com).
"Even when we lose a game, he has some great ideas on and off the pitch. He is experienced enough to think about what went wrong, you don't have to tell him."
Mertesacker felt Cech was back to his best when the Gunners beat Crystal Palace 2-1 in a hard-fought away match on Sunday.
"My feeling is he comes back even stronger, so there is no doubt he will be a great addition for us. Even when you are experienced, sometimes mistakes happen," the 30-year-old said.
The former Werder Bremen defender said he was already communicating well with Cech on the field.
"The interaction between the goalkeeper and the back four has to be top to compete in the Premier League," the German World cup winner said.
"Petr came and had that understanding from the start, we both communicate well and understand each other as someone who has to talk and is really responsible.
"We match our ambitions on the pitch and so it is great to communicate with him."
Arsenal host Liverpool in the Premier League on Monday and Mertesacker is aware of the threat the Merseyside club pose after investing heavily on the squad.
He, however, disagrees that it is a must-win game.
"That (a must-win game) is not the pressure we put on ourselves, but obviously it is a very important game," Mertesacker said.
"Liverpool is an opponent which has invested a lot of money and will be great competition to play against, especially at home.
"We want to give something back to our crowd after the (bad) start."
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Sudipto Ganguly)
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