Naomi Osaka marks return from illness with win over Zarina Diyas

U.S. Open champion Naomi Osaka showed no signs of fatigue as she marked her return from illness with a 6-4 6-3 win over Zarina Diyas in the China Open first round on Monday.

Osaka, 20, who skipped last week's Wuhan Open due to a viral infection, broke her Kazakh opponent five times in the 68-minute match to book a second-round clash with Danielle Collins.

The world number six from Japan broke Diyas in the ninth game before claiming the opening set and she reeled off four games in a row before closing out the victory.

Australian Open champion Caroline Wozniacki beat Switzerland's Belinda Bencic 6-2 6-3 while former world number one Garbine Muguruza of Spain dispatched Russian Ekaterina Makarova 6-0 6-4.

American Madison Keys pulled out with a knee injury before her match against Anastasija Sevastova, local hope Zhang Shuai upset 15th seed Elise Mertens 6-1 3-6 6-3 and seventh seed Karolina Pliskova cruised past Australian Samantha Stosur 6-4 6-4.