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Per Mertesacker admits his Arsenal side have to improve defensively to be serious title challengers this season.

Arsene Wenger's men have conceded three goals in their opening two games of the campaign, haven't kept a clean sheet in either game and have looked uncharacteristically shaky at the back - despite the much-celebrated arrival of iconic Chelsea keeper Petr Cech.

Mertesacker says it will take time for their new No 1 to form an understanding with his back four after over a decade at Stamford Bridge.

Defender Mertesacker said: “Even when you are experienced, sometimes mistakes happen. But the interaction between the goalkeeper and the back four has to be top to compete in the Premier League.

“You never know, sometimes it takes longer than you think. Let’s have a good start first, then we can analyse.

(Image: Mike Hewitt/Getty)

“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. He is very experienced.

“You can feel that he has lots of things to say. In the dressing room he gives us a great lift - even when we lose a game, he has some great ideas on and off the pitch.

“He is very important for us and a good addition. He is experienced enough to think about what went wrong - you don’t have to tell him.

"My feeling is he comes back even stronger, so there is no doubt he will be a great addition for us.”

Arsenal were shell-shocked after losing their season-opener at home to West Ham, and only just scraped through to victory away to Crystal Palace on Sunday.

In pictures — Crystal Palace 1-2 Arsenal:

Mertesacker admits the players held their own “very important” dressing room inquest after that Hammers setback.

He says it served as a “reminder” just how tough it will be to challenge for the title - and says they must get a win when Liverpool visit next Monday.

“Obviously, when everything goes very smooth in pre-season, you avoid those talks which are sometimes very important. That was the case last week," said the 30-year-old German.

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“Last week was a reminder to ourselves to just be aware - everywhere in the Premier League there is big competition. It (Liverpool) is a Monday night game, so everyone will have played (their games) in front of us. It is important that you get some points to get in a better situation.

“It is the start of the season and we praised ourselves for a good end to last season, but we wanted to start stronger.

“Liverpool is obviously a very important game. It 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 start against West Ham.”