Sam Sumyk, the coach of Victoria Azarenka, says fatigue was a factor in the final set of the Belarusian's 7-5, 6-7 (6), 6-1 loss to Serena Williams in the U.S. Open final. Azarenka came back from a 1-4 deficit to win the second set, but lost the last five games of the third set.

“She ran out of little bit of gas to keep pushing from behind,” Sumyk told TENNIS.com. “When you run out of energy it’s better to lead because that gives a little boost, but to push, push, push always to come back drains you.”

Sumyk also said that Azarenka could have hit better shots and made better decisions in the match. The world No. 2 defeated Williams in two hard-court finals coming into New York, but has yet to beat the now 17-time Grand Slam champion at a major.

“It was never a problem to play Serena,” he said. “We are the first ones to recognize what a great player Serena is, but it’s not something were scared of. It’s a privilege when you play the great players. Vika wants to be challenged by the best and get better herself. I hope they play a lot more against each other.”