Belinda Bencic and Timea Bacsinszky were each forced to retire from their first-round matches on day one of the Wuhan Open.
Bencic was 4-3 up in the second set against ninth seed Svetlana Kuznetsova, who had taken the opener 6-3, when she was forced to withdraw after falling and injuring her back.
Twelfth seed Bacsinszky, meanwhile, was unable to complete her match against Louisa Chirico and retired at 6-3 4-3 down.
The only other seed in action on Sunday, Roberta Vinci, recorded an impressive straight-sets win over Olympic champion Monica Puig.
There were also first-round wins for Yaroslava Shvedova, Irina-Camelia Begu, Yanina Wickmayer, Ekaterina Makarova, Lucie Safarova, Laura Siegemund and Katerina Siniakova.
BENCIC INJURY WOES CONTINUE
Switzerland's Bencic has been hampered by injuries to her back and wrist in 2016.
After retiring on Sunday, the 19-year-old indicated she had hurt the same area in her lower back that had previously caused her problems this year.
It remains to be seen whether a lengthy lay-off is now in store for Bencic, who was ranked seventh in the world in February, but is now down at 26th.
RADWANKSA, HALEP, PLISKOVA LEARN SECOND-ROUND OPPONENTS
Third seed Agnieszka Radwanska will face Makarova in round two after the Russian dropped just three games in thrashing Sabine Lisicki.
Begu's three-set triumph over Elizaveta Kulichkova set up an all-Romanian tie with Simona Halep, while Karolina Pliskova will begin her campaign against Safarova - a 7-5 6-3 victor over Varvara Lepchenko.
WOZNIACKI AIMING TO FOLLOW UP TOKYO TRIUMPH
A day on from her drought-breaking victory in the final of the Pan Pacific Open, Caroline Wozniacki will begin her bid for glory in Wuhan on Monday against 16th seed Samantha Stosur.
The opening matches for Halep and Pliskova shape as other potential highlights on day two, while seventh seed Carla Suarez Navarro faces Yanina Wickmayer.