Serena Williams' was forced to withdraw from the second round of the Wuhan Open as several big names tumbled on Tuesday.
World number one Williams was making her first appearance since winning her 18th grand slam title at the US Open earlier this month, but pulled out of the WTA Premier hard-court event in China when leading Alize Cornet 6-5 in the opening set.
The reason for the American's withdrawal was not immediately obvious, although the WTA later confirmed that a viral illness curtailed her participation.
Williams' exit opens up the draw and Cornet will now meet Kirsten Flipkens for a spot in the quarter-finals after the Belgian defeated Jarmila Gajdosova in three sets.
Earlier, there had already been a shock as second seed Simona Halep fell to a 2-6 6-2 6-3 loss to Garbine Muguruza.
It was the first time the two had met on Tour, and Halep lived up to her world number two status by clinching the first set in 35 minutes.
However, the Romanian was punished for 38 unforced errors as Muguruza stormed to a 4-0 lead in the second before levelling the tie, then winning the last four in the third to wrap up the match.
Elina Svitolina stands in Muguruza's way of a last-eight spot following her 7-6 (7-3) 6-3 triumph over Sabine Lisicki.
Halep was not the only big-name second-round casualty, as Jelena Jankovic withdrew with a back injury when trailing Coco Vandeweghe 4-1 in the first set, while fellow seeds Sara Errani, Ekaterina Makarova and Andrea Petkovic were ousted by Alison Riske, Timea Bacsinszky and Karolina Pliskova respectively.
Petra Kvitova is now the highest seed left in the competition and the Czech, seeded third, was in fine form in her 6-3 6-0 rout of Karin Knapp.
Meanwhile, US Open runner-up Caroline Wozniacki, seeded eighth, found the going tough as she was taken the distance in a 6-1 3-6 7-6 (7-4) victory over Carla Suarez Navarro.
Like Wozniacki, Eugenie Bouchard and Angelique Kerber, the sixth and seventh seeds, needed three sets in respective win against Mona Barthel and Zarina Diyas.
Elsewhere, there were also wins for Barbora Zahlavova-Strycova and Casey Dellacqua.