CHARLESTON   -  Defending champion Kiki Bertens and third-seeded Aryna Sabalenka, both among the top 10 players in the world, lost Thursday at the Volvo Car Open. Top-seeded American Sloane Stephens, ranked eighth in the world, needed three sets to advance over 14th-seeded Ajla Tomljanovic of Australia 4-6, 6-4, 6-4 to reach the quarterfinals.

Bertens, the second seed of the Netherlands who’s No. 6 in the WTA rankings, fell to 15th-seeded Maria Sakkari of Greece 7-6 (8), 6-3. Sabalenka, the world’s 10th ranked player from Belarus, was defeated by Monica Puig of Puerto Rico 6-2, 7-5 at the season’s first clay-court event.

Others advancing to the final eight were No. 5 seed Caroline Wozniacki of Denmark, eighth-seeded American Madison Keys, No. 9 seed Belinda Bencic of Switzerland, the 11th-seeded American Danielle Collins and 16th-seeded Petra Martic of Croatia.