Their dominant 5-1 victory over Manchester City on Sunday has boosted morale and closed the gap to leaders Liverpool.
Despite trailing 2-0 from the first leg in the cup, Martinelli insists the squad is motivated and ready for the challenge.
“It is hard to play there (at St James’ Park),” he said after the 5-1 win over City.
“They are a really good side, but we have full confidence in our squad and we trust ourselves.
“It is going to be another battle there. We know how difficult it is to play there. But, as I said, we have an amazing team and we trust ourselves. We are going to go there to win the game.
“We know our qualities. It is not because we lost 2-0 here in the last game, we are going to go there just to play now.
“We are going to go there to win the game and to score three, four, five. Let’s see, the game is going to be really hard, for sure. But we are going to try our best to win the game.”