World number three Maria Sakkari was knocked out of the US Open in the second round by China's Wang Xiyu.
Greece's Sakkari, who reached the semi-finals in New York last year, won the first set but could not capitalise on her lead, losing 3-6 7-5 7-5.
It is the the third time Sakkari has lost to a player ranked outside the world top 50 at a Grand Slam this year.
Wang, meanwhile reaches the third round of a major for the first time.
There were fewer second-round troubles for world number five Ons Jabeur, however, as she battled to a straight-sets win over American Elizabeth Mandlik.
Tunisian Jabeur, who has never progressed past the third round at Flushing Meadows, won 7-5 6-2 though saw Mandlik twice go up a break and had to save a set point in the first set.
The Wimbledon finalist will next face Shelby Rogers, who defeated Slovakia's Viktoria Kuzmova 7-5 6-1.
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