Wuhan - Top seed Serena Williams had to be helped from the court as she retired ill during her first set at the inaugural Wuhan Open in China on Tuesday.The world number one had her temperature and blood pressure checked before retiring while 6-5 up against France's Alize Cornet, after just over an hour on court.
It brought an abrupt end to Williams' first match since she won her 18th Grand Slam title at the US Open in New York two weeks ago.
The incident is another blow for the Wuhan Open after poster girl and hometown hero Li Na quit tennis on the eve of the tournament.
"I'm sorry to all the fans in Wuhan that I had to retire from my match against Alize today," she said later. "I felt dizzy and nauseous in the first set and unfortunately couldn't continue.
"The tournament organisers have done an amazing job preparing the facilities for this year's event and I really hope to come back to the Wuhan Open in 2015."
The retirement meant France's Cornet, who beat Williams at Dubai and Wimbledon, becomes the first player to win three matches against her in a season since Justine Henin in 2007.
Williams, 32, was not the only high-profile retirement. Former world number one Jelena Jankovic went out with a back injury while 4-1 down against Coco Vandeweghe.
An ultra-aggressive Garbine Muguruza ousted Romanian second seed Simona Halep 2-6, 6-2, 6-3 as yet another top-10 player was sent packing.
But Danish world number seven Caroline Wozniacki beat Spain's Carla Suarez Navarro 6-1, 3-6, 7-6 (7/4) to safely reach the third round.
World number six Agnieszka Radwanska was ousted by Caroline Garcia on Monday from a tournament which is now missing a swathe of seeded players.
Italian Sara Errani, seeded 11, 13th seed Russian Ekaterina Makarova and 16th seed German Andrea Petkovic all fell in the second round.
World number four Maria Sharapova remains and must feel in with a good chance of winning the $2.4 million tournament which reaches its climax on Saturday.
The Russian led the tributes to two-time Grand Slam champion Li when she announced she was bowing out of the game last week.
The 32-year-old Li was the first Chinese to win one of tennis's big four singles titles at the French Open in 2011. She is credited with sparking a surge in interest in the sport in her homeland.