Sun Yang of China reacts after winning the men's 800m freestyle final at the Aquatics World Championships in Kazan, Russia, Aug 5, 2015. [Photo/Agencies]

"I know it would be a tough match," said Sun, who won the 400m free title last Sunday and took a silver in the 200m on Tuesday. "I expected to win before the match and I did it. I know the following race will be very difficult, and I will try my best."

He will take part in the men's 1500m free on Saturday.

"I am very tired as it is the fourth competition day in swimming and I had races every day," he added. "I can take some rest in the following two days."