The Volvo Car Open will not have a repeat champion this year.
No. 5 seed Julia Goerges eliminated defending champ Daria Kastkina by 6-4, 6-3 in Friday's first quarterfinal match at the Family Circle Tennis Center on Daniel Island.
Crowd favorite Madison Keys advanced to the semifinals as well, surviving a tough 2-hour and 14 minute battle with Bernarda Pera.
Keys, the No. 7 will face No. 12 Kiki Bertens in the semis. Bertens eliminated No. 14 Alize Cornet, 6-2, 7-5, in Thursday's late match.
Goerges, a 29-year-old German ranked No. 13 on the WTA Tour, will face No. 17 Anastasija Sevastova of Latvia, a 6-4, 6-0 winner over Kristyna Pliskova, in Saturday's semifinals.
Goerges has won five WTA singles titles in her career, including a win over Caroline Wozniacki in the finals at Auckland earlier this year. This is her best performance in five appearances in Charleston.
Unable to defend her VCO crown, the 20-year-old Kasatkina was emotional at match's end.
"I was really upset after the match," the Russian said. "So yeah, I was not able to hold my tears after the match. So I just went to yeah, it's tough, but I'm happy that I have this experience now, and I went through this and I'm pretty sure next time is going to be much easier."
Keys did not have it easy against fellow American Pera, a 23-year-old ranked No. 101 in the world.
Keys, ranked No. 14 and seeded seventh here, was cruising along after winning the first set 6-2, but Pera took the second set in a tie breaker. Keys finally finished off Pera, who is ranked No. 101 in the world, 7-5, in the third set.
"I had to be proud of what I did on the court today," said Keys, a finalist at the U.S. Open last year. "And I knew if I didn't leave it all out there, I would have been really mad at myself later."
VCO officials said storms forecast for Saturday afternoon could impact Saturday's schedule, including the Invesco Legends men's event set for Saturday night.
The priority will be completing the women's semifinals, which means the Invesco Legends event could be moved to Sunday night.