Defending champion Daria Kasatkina progressed to the last eight at the Charleston Open but Japanese sensation Naomi Osaka crashed out.
Kasatkina – the Russian third seed – cruised past Irina-Camelia Begu 6-2 6-1 at the WTA Tour tournament Thursday.
The Indian Wells runner-up needed little more than an hour against the 13th seed to move into the quarter-finals.
Standing in the way of Kasatkina and the semi-finals is Julia Goerges, who upstaged Indian Wells champion Osaka.
"She's a really tough opponent because she's very aggressive, she's serving well," Kasatkina said. "She has a very aggressive forehand, very solid backhand. So to beat her for sure I have to show something special and to play not like go on court just to play."
Osaka – victorious against 23-time grand slam winner Serena Williams in Miami – was sent packing following a 7-6 (7-4) 6-3 loss to Germany's Goerges.
Anastasija Sevastova also advanced with a straight-sets win over Australian star Ashleigh Barty, while Madison Keys won through despite a scare against Camila Giorgi.
At the Monterrey Open, Wimbledon champion and top seed Garbine Muguruza reached the quarter-finals.
Muguruza was a class above in a 6-2 6-3 triumph against Alison Riske, after claiming four breaks while tallying 24 winners in Mexico.
The Spaniard, who saved three break points in the opening game, will meet eighth seed Ajla Tomljanovic in the quarters, while third seed Lesia Tsurenko withdrew before her match against Danielle Collins.