Top-seeded Eugenie Bouchard of Canada and second-seeded Angelique Kerber of Germany lost in the second round of the Diamond Games on Thursday.
Bouchard double-faulted nine times in a 4-6, 6-1, 6-2 defeat to Germany's Mona Barthel, while qualifier Francesca Schiavone — a former French Open champion — needed under one hour to beat Kerber 6-1, 6-1.
Schiavone next plays fifth-seeded Carla Suarez Navarro of Spain in the quarterfinals, after she rallied past Monica Niculescu 4-6, 6-0, 6-2.
Fourth-seeded Lucie Safarova of the Czech Republic; sixth-seeded Dominika Cibulkova of Slovakia and No. 8 Karolina Pliskova of the Czech Republic advanced to the quarterfinals.
Safarova beat France's Kristina Mladenovic 6-4, 6-1; Cibulkova downed Dutch qualifier Indy de Vroome 6-3, 3-6, 6-2 and Pliskova won 6-3, 6-3 over Germany's Annika Beck.