US Open champion Serena Williams has lost in the second round of the Wuhan Open in China, retiring after 11 games and dropping a third match to Alize Cornet this year.

Williams had just converted a break point for a 6-5 lead in the first set when she asked for treatment beside the court. Organisers later said Williams withdrew due to a viral illness.

Cornet beat Williams at Dubai in February and had a third-round win at Wimbledon. The Frenchwoman is the first player since Justine Henin in 2007 to beat Williams three times in year, the WTA said, and has improved to 3-3 in career meetings with the most dominant woman in tennis.

The tournament’s top two players were eliminated within hours, with Williams exiting after Garbine Muguruza of Spain beat No. 2-ranked Simona Halep of Romania 2-6 6-2 6-3.

Muguruza, who beat Williams in the second round at the last French Open, dropped the first set in 35 minutes but rallied to win the first four games of the second set and the last four games of the third to advance at the inaugural Wuhan Open.

It was a mixed day for Australians at the tournament, with Casey Dellacqua beating Anastasia Pavlyuchenkova of Russia, 7-6 (9-7) 6-7 (7-5) 6-1.

However, Belgium’s Kirsten Flipkens defeated Jarmila Gajdosova 6-3 3-6 6-3.

In other matches, No. 10 Jelena Jankovic was trailing 4-1 when she retired against American player Coco Vandeweghe due to a back problem, and Alison Riske of the United States recovered an early break to beat No. 11 Sara Errani of Italy 6-4 6-4.

Swiss qualifier Timea Bacsinszky defeated No. 13 Ekaterina Makarova 6-4 6-1 and Karolina Pliskova of the Czech Republic had a 6-4 6-4 win over No. 16 Andrea Petkovic of Germany.

Eighth-seeded Caroline Wozniacki, however, held off Carla Suarez Navarro of Spain 6-1 3-6 7-6 (7-4).