Havertz finished a superb pass from Martinelli for the 1-0 quarterfinal first-leg win after the pair came on in the second-half.
“I've said that about 80 per cent of the goal goes to him,” Havertz said afterwards. “I was there to finish it off. I but it was a top assist from him, I saw him and he just played the perfect pass and it was a good goal."
Havertz also heaped praise on Gunners goalkeeper David Raya for his performance on the night.
"He's unbelievable - I still think people underestimate him in the football world, but for the last two years, I don't know, maybe he's been the best 'keeper in the world and we're all glad to have him here."
The Germany attacker continued: "Yeah I think we needed that as we were all frustrated with how the last couple of weeks went, but it's time to move forward, it's time to be positive, and it's time to all stick together as a group - as players, staff, fans, we're all in this together and we still can make something happen this year.
"It can be something very special, that's what we're going to go for, and now it's time to win games."