Updated

Top-ranked Serena Williams is out in the second round of the new WTA event at Wuhan, retiring after 11 games on Tuesday and dropping a third match to Alize Cornet this year.

Williams, who won the U.S. Open just over two weeks ago, was leading 6-5 when she was treated beside the court. The reason for the retirement was not immediately clear.

Cornet beat Williams at Dubai in February and had a shock third-round win at Wimbledon.

The tournament's top two seeds were eliminated within hours, with Garbine Muguruza of Spain beating No. 2 Simona Halep of Romania 2-6, 6-2, 6-3.

Muguruza, who beat Williams at the 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.