Germany's Julia Goerges continued her strong season by defeating defending champion Daria Kasatkina to reach the semi-finals of the WTA tournament in South Carolina.
German fifth seed Goerges overpowered the third-seeded Kasatkina of Russia 6-4 6-3 with nine aces.
She won 84 per cent of her points on her first serve to advance to the final four at the season's opening clay-court tournament.
Goerges will face Latvian eighth seed Anastasija Sevastova, who ended the surprise run of unseeded Kristyna Pliskova 6-4 6-0.
Madison Keys, the US Open runner-up last year, was pushed to a tough third set before she prevailed 6-2 6-7 (5-7) 7-5 in an all-American quarter-final with left-handed Bernarda Pera.
The seventh-seeded Keys will face Kiki Bertens, who overcame leg pain to dispatch France's Alize Cornet 6-2 7-5 in their evening quarter-final.
