The Turkey international has struggled to replicate the performances he put in during his first spell for the club since leaving for Real Madrid in 2011.
A subsequent loan move to Liverpool failed to bear fruit, but he is confident that he is now approaching top form, having scored twice in the rout of Christian Streich's side.
"I think I've been improving bit by bit since coming back to Dortmund, even in training. Now the self confidence is slowly returning and I’m more comfortable with my game too," he told Bundesliga.com
"My game is all about risks and I’m allowed to show that here. The coach doesn't only allow it, he actually demands it. That type of faith from the coach does me and my game the world of good."