NEW YORK (AP) — Bothered by pain in his back, ribs and cramping legs, Novak Djokovic was face-down beside the court in Arthur Ashe Stadium, getting massaged by a trainer.

Having dropped a set against defending champion Rafael Nadal, Djokovic’s grip on the U.S. Open final appeared to be starting to slip away and, worse, his body was breaking down.

His confidence? That, more than any particular stroke, is what Djokovic credits with transforming him from a top player to a great one — and it never wavered one bit Monday night.

Producing a nearly perfect performance to match his nearly perfect season, the No. 1-ranked Djokovic returned brilliantly, whipped winners from all angles and beat No. 2 Nadal 6-2, 6-4, 6-7 (3), 6-1 in a match chock-full of lengthy, mesmerizing points to earn the first U.S. Open championship of his career and third Grand Slam trophy of 2011.

“In big matches, the winner is decided by small margins, a couple points. I guess the winner is the one who believes in victory more,” said Djokovic, who is 64-2 with 10 tournament titles.

“I guess it just clicked in my head. Through the last couple of years, I didn’t change my game in any major way. … But I’m hitting shots that maybe I wasn’t hitting,” he explained. “I’m going for it. I’m more aggressive.”