Czech 10th seed Karolina Pliskova needed five match points before finally clinching victory over former champion Venus Williams at the US Open.
Pliskova, 24, was broken when serving for the match at 40-0 but recovered to win 4-6 6-4 7-6 (7-3) and reach her first Grand Slam quarter-final.
Romanian fifth seed Simona Halep beat Spain's Carla Suarez Navarro 6-2 7-5.
In the men's draw, both Swiss fourth seed Stan Wawrinka and Argentina's Juan Martin del Potro progressed.
Wawrinka saw off Ukraine's Illya Marchenko 6-4 6-1 6-7 (5-7) 6-3 to set up a quarter-final against 2009 champion Del Potro, who led Dominic Thiem 6-3 3-2 when the Austrian retired with a knee injury.