Garbine Muguruza retires with cold; Sloane Stephens falls in straight sets

BEIJING -- Top-ranked Garbine Muguruza retired from her opening match at the China Open with a cold Monday.

Muguruza dropped the first set 6-2 and was trailing 2-0 against Barbora Strycova when she decided to stop.

"I couldn't perform today," said the Spaniard, who said she picked up a virus at the Wuhan Open last week but wanted to try to play despite her illness. "I don't want to retire before the tournament starts for me."

Also, US Open champion Sloane Stephens lost to Christina McHale 6-3, 6-0.

"It was a tough day," Stephens said. "There's not really much to say about. Obviously not a great match, so just forget about it and try to move on."

In other women's matches, former No. 1 Caroline Wozniacki beat Anastasia Pavlyuchenkova 6-2, 6-2, while Peng Shuai, Elena Vesnina, Elise Mertens, Coco Vandeweghe and Alize Cornet also won.

Men's winners included fifth-seeded Roberto Bautista Agut, Mischa Zverev, Steve Darcis, Fabio Fognini and Aljaz Bedene.

Top-ranked Rafael Nadal will open against Lucas Pouille on Tuesday. The Frenchman beat Nadal in their previous meeting last year.