Ozil saw a penalty saved against Marseille on Tuesday but he quickly responded by providing the assist for Jack Wilshere's second goal.
"He has made good progress," Mertesacker told arsenal.com. "He is in good form and you can see that. Especially against Marseille he was always a threat and he never gave up after the penalty that he missed.
"We are very delighted with him, especially in the transition from defence to offence. He is the one who always goes deep all of the time.
"He gets himself into good positions so the goals will come for sure. He moves well between the lines so it is always difficult to defend against him. When the centre back comes out with him, there is always space for others to move into.
"He helps us create more chances. We are playing well as a team and we should continue that in the Champions League and the Premier League."
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