American Amanda Anisimova rallied after losing the opening set to beat top-seeded Aryna Sabalenka of Belarus 3-6, 6-4, 6-3 and reach the quarterfinals of the Charleston Open.
In more surprises, Ekaterina Alexandrova of Russia and CoCo Vandeweghe of the United States both reached the final eight with wins over seeded opponents on Thursday.
Alexandrova defeated No 3 seed Karolina Pliskova 6-3, 6-1 while Vandeweghe topped countrywoman and sixth-seeded Jessica Pegula 6-4, 3-6, 6-4.
Paula Badosa, the second seed, dropped her first set before fighting off Claire Liu for a 3-6, 7-6, (8) 6-1 victory to move into the quarters. No 10 seed Belinda Bencic, the Olympic Gold medalist last summer, defeated ninth-seeded Madison Keys 6-4, 6-4.
Fourth-seeded Ons Jabeur did double duty, winning twice on Thursday to make the quarters. Jabeur's match with Emma Navarro was halted on Wednesday because of severe weather with her leading 6-3, 5-2. The two returned on Thursday where Jabeur won four straight points to close things out. Later, Jabeur eliminated Irina-Camelia Begu of Romania 6-3, 6-2. Anhelina Kalinina of Ukraine topped No 12 seed Alize Cornet of France 7-6 (5) 7-5.