No.2-ranked Simona Halep lost her opening match at the Wuhan Open, dismantled by Daria Kasatkina 6-2 6-1 on Tuesday.
Halep received a bye into the second round. She broke Kasatkina early but the Russian dominated thereafter.
It was Kasatkina's third win over a top-five player, after two wins over then-No.1 Angelique Kerber this year.
"The game was much more difficult than the score is," Kasatkina said.
Halep had a chance this week to supplant Garbine Muguruza as No.1 by reaching the final with other results going her way.
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No.4 Karolina Pliskova kept alive her shot at No.1 by beating local Shuai Zhang 6-4 3-6 6-4. To regain the No.1 ranking, Pliskova must win the Wuhan title and hope Muguruza loses before the semifinals. Muguruza was in action late.
"I always want to play better than I did last year; I already won one round so hopefully I can win one more," Pliskova said.
Another Russian, two-time major champion Svetlana Kuznetsova, lost to Alize Cornet of France 6-3 6-3.
Three other seeds advanced: No.7 and 2016 finalist Dominika Cibulkova, No.8 Jelena Ostapenko, and No.9 Agnieszka Radwanska.
Radwanska will now play Ashleigh Barty for a spot in the last eight after the Australian upset Johann Konta on Monday.
Ostapenko came back to beat Barbora Strycova 2-6 7-5 6-3 and Radwanska saw off Julia Goerges of Germany 7-5 7-5.
Ekaterina Makarova of Russia, Caroline Garcia of France, Wang Qiang of China, and Varvara Lepchenko of the US were also winners on Tuesday.
