Alison Riske inflicted another first-round defeat on Angelique Kerber as the former world number one crashed out of the Zhengzhou Open in China.
American Riske, who was a surprise quarter-finalist at Wimbledon in July, came from behind to beat Germany's three-time grand slam winner 5-7 6-4 7-6 (8-6) on Tuesday.
It means Kerber has lost her opening match at four successive tournaments, last enjoying a victory in the first round of Wimbledon.
Former French Open champion Jelena Ostapenko, who beat Riske in the second round of the US Open two weeks ago before falling in round three, recovered from a mid-match slump to beat China's You Xiaodi in the first round in Zhengzhou.
Latvian Ostapenko, who has nosedived from 22nd to as low as 83rd in the WTA singles rankings this year – she is currently at 75 - was a 6-3 0-6 6-2 winner against qualifier You.
France's Kristina Mladenovic beat Kerber in the first round of the US Open, before falling in round two. Mladenovic began her campaign in Zhengzhou with a comfortable 6-2 6-3 win against Duan Ying-Ying.
Fiona Ferro, who beat Mladenovic in New York, started out at the Chinese event with a 6-2 6-3 success against Yang Zhaoxuan, while Alize Cornet and Ajla Tomljanovic also made it safely through to round two.