The 20-year-old goalkeeper put in an assured performance on his debut for the Club in last month's 6-1 victory against Coventry City.
"The day before [the Coventry match], I was a bit nervous and I wanted to play," Martinez told Arsenal Player. "But when we went to warm up, I was feeling so confident and focused on the game. When the game started the ball was passed to me, I passed it back and thought 'this is my game'.
"Everyone said I had no chance with the goal and it was a great ball from the right wing. But if you're a goalkeeper, you want to keep clean sheets. I didn't and I wasn't too happy.