Venus Williams suffers surprise defeat to Naomi Osaka in Hong Kong

Osaka is one of the most exciting young players in the women's game and the Japanese-American achieved her career-best win ranking-wise with a 7-5 6-2 victory over world number five Williams.

It ended a run of five straight losses for Osaka, who was beaten by Williams at Wimbledon before seeing off defending champion Angelique Kerber at the US Open.

The 19-year-old next faces sixth seed Anastasia Pavlyuchenkova, who defeated Jacqueline Cako 7-6 (7/3) 6-1, while seventh seed Daria Gavrilova was a 6-1 2-6 6-2 winner over Shelby Rogers.

At the Tianjin Open, there were wins for Maria Sharapova and Sara Errani in her first WTA Tour match following a doping ban.

The Italian was suspended for two months after testing positive for letrozole. Errani successfully convinced the International Tennis Federation that she had ingested the substance unknowingly after her mother's cancer medication contaminated a batch of tortellini.

After negotiating qualifying, Errani, a former world number five now ranked 280, eased to a 6-2 6-1 victory over Kateryna Kozlova.

Following two days of rain, all first-round matches were played on Wednesday.

Sharapova defeated Irina-Camelia Begu 6-4 6-2 but second seed Petra Kvitova was knocked out 6-4 5-7 6-4 by Zhu Lin.

Fourth seed Donna Vekic also fell along with eighth seed Alison Riske, the runner-up to Peng Shuai 12 months ago.

Third seed Peng began her title defence with a 6-2 7-6 (7/5) victory over Guo Hanyu.