US 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.

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 Japanese world No.6 broke Diyas in the ninth game before claiming the opening set and she reeled off four games in a row before closing out victory.

Australian veteran Samantha Stosur suffered a straight-sets defeat to Karolina Pliskova.

Stosur began strongly and built a 4-1 lead before the Czech reeled off nine straight games and eventually ran out a 6-4 6-4 winner.

It was the same scoreline Pliskova achieved in their only previous meeting with Stosur in the first round at China’s Wuhan Open in 2014 and has set up a second-round tie with Belarusian Aliaksandra Sasnovich.

“I’m not exactly sure why things turned so dramatically in the end there,” Stosur said.

“I was always expecting her to improve her level – she’s a good player so she’s gonna find a way.”

Stosur’s compatriot Daria Gavrilova, who put out two-time Wimbledon winner Petra Kvitova 6-2 6-1 in her opener, faces Dominika Cibulkova in the second round on Tuesday.

Australian Open champion Caroline Wozniacki beat Switzerland’s Belinda Bencic 6-2 6-3 while former world No.1 Garbine Muguruza of Spain dispatched Russian Ekaterina Makarova 6-0 6-4 and now plays newly crowned Wuhan champion Aryna Sabalenka.

There was delight for the home fans as Chinese world No.45 Shuai Zhang beat Belgium’s Elise Mertens 6-1 3-6 6-3, while Carla Suarez Navarro and Petra Martic were among the other first-round winners.

In second-round action, Donna Vekic beat Tunisian qualifier Ons Jabeur 7-6 (7-5) 6-4, Julia Goerges advanced when opponent Laura Tsurenko was forced to retire at 6-4 4-6 2-2. American Madison Keys pulled out with a knee injury before her match against Anastasija Sevastova.