CHARLESTON, S.C. (AP) - 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.
RESULTS - APRIL 4, 2019
Singles - Third Round
 S. Stephens (USA) d  A. Tomljanovic (AUS) 46 64 64
 M. Sakkari (GRE) d  K. Bertens (NED) 76(8) 63
M. Puig (PUR) d  A. Sabalenka (BLR) 62 75
 C. Wozniacki (DEN) d  M. Buzarnescu (ROU) 64 36 63
 M. Keys (USA) d  J. Ostapenko (LAT) 75 62
 B. Bencic (SUI) d T. Townsend (USA) 62 75
 D. Collins (USA) d K. Kanepi (EST) 76(1) 61
 P. Martic (CRO) d J. Pegula (USA) 26 63 62
Doubles - Quarterfinals
A. Friedsam (GER) / S. Sorribes Tormo (ESP) d  N. Melichar (USA) / K. Peschke (CZE) 76(1) 61
 A. Groenefeld (GER) / A. Rosolska (POL) d S. Aoyama (JPN) / L. Marozava (BLR) 60 61
ORDER OF PLAY - FRIDAY, APRIL 05, 2019
VOLVO CAR STADIUM start 10:45 am
[WC] C. Beck (USA) / E. Navarro (USA) vs  L. Hradecka (CZE) / A. Klepac (SLO)
Not Before 1:00 pm
 B. Bencic (SUI) vs  P. Martic (CRO)
 C. Wozniacki (DEN) vs  M. Sakkari (GRE)
 S. Stephens (USA) vs  M. Keys (USA)
Not Before 7:00 pm
M. Puig (PUR) vs  D. Collins (USA)