The Gunners lost the first leg of their round of 16 clash 1-0 away from home through a 94th minute Galeno strike.
While Martinelli acknowledged they were not good enough in the first leg, he believes they can progress.
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Martinelli told TNT Brazil: "We have to minimize the mistakes and score the goals we need.
"We are confident. We know the potential of our team. We are going to play at home and we are going to go all out to win the game.
"Sometimes you don't lose Championships in big games, but in the game against lesser teams. I think you have to take every game seriously and be very focused, because every game is important."