Lesia Tsurenko upset second-seeded Coco Vandeweghe on Wednesday to reach the quarter-final of the Kremlin Cup in Moscow, while top-seed Kristina Mladenovic was knocked out by Aliaksandra Sasnovich.
Tsurenko, who took control of the match early in the first set, defeated Vandeweghe 7-5, 1-6, 6-2 in just over two hours.
She will face seventh-seeded Julia Goerges, who beat Yulia Putintseva in 6-3 6-3 on Wednesday.
Sasnovich capitalised on Mladenovic's 16 double faults to win the match 6-2 2-6 6-2 and earn a spot in the quarter-final where she will face Russia's Daria Kasatkina, who beat Katerina Siniakova 6-2 6-3.
Also on Wednesday Irina-Camelia Begu upset fourth-seeded Anastasija Sevastova, winning 6-4 6-3.
Begu will face Belarusian qualifier Vera Lapko in the quarter-final after she beat Daria Gavrilova 6-3 3-1 after the Australian retired hurt.
After defeating Maria Sharapova in front of a jubilant crowd on Tuesday, Magdalena Rybarikova retired hurt after the first set to let France's Alize Cornet through to the quarter-final.
Cornet will face Russia's Natalia Vikhlyantseva, who upset third-seeded Elena Vesnina 7-6 6-4.