Britain's Johanna Konta won a hard-hitting contest against Slovakian Dominika Cibulkova to reach the Cincinnati Open quarter-finals.
The seventh seed won 6-3 6-4 to reach the last eight for the first time, setting up a rematch of her Wimbledon quarter-final against Simona Halep.
Romanian second seed Halep beat Latvian 15th seed Anastasija Sevastova 6-4 6-3.
Rain halted several third round ties, with top seed Rafael Nadal yet to start his match against Albert Ramos-Vinolas.
The winner of that all Spanish contest will face either Ivo Karlovic or Nick Kyrgios in the last eight - the Croatian led 4-3 when that match was postponed - with the victors due to play twice on Friday.
Bulgarian seventh seed Grigor Dimitrov beat Argentine Juan Martin del Potro for the first time in six attempts, coming through 6-3 7-5 to set up a quarter-final against Japan's Yuichi Sugita.
In the other men's quarter-finals, Austrian third seed Dominic Thiem will face Spain's David Ferrer, while American John Isner takes on compatriot Jared Donaldson.
Konta sees off spirited Cibulkova
Konta, 26, did well to win a match that was far tougher than the straight-set scoreline suggests and break new ground in Cincinnati.
Five double-faults and a first-serve percentage of just 54% meant the Briton had to work harder than usual in her service games, with Cibulkova teeing off aggressively on the return.
Konta took the first set with two breaks of serve to one and looked to have the match well under control when she broke at the start of the second set.
However, Cibulkova refused to submit and had three break points for a 4-2 lead as a gripping set unfolded.
Konta clung on and grabbed her chance with a deep return on break point at 4-4 before serving out for a fine win, finishing with 24 winners to Cibulkova's 10.
Muguruza back from the brink
Wimbledon champion Garbine Muguruza saved three match points on her way to beating American Madison Keys for the first time in four meetings.
The Spanish fourth seed came through 6-4 3-6 7-6 (7-3) to set up a quarter-final against Russian eighth seed Svetlana Kuznetsova, who beat Spain's Carla Suarez Navarro 6-2 6-4.
"You never knew who was going to win until the last point," said Muguruza. "I had match points against me so it was really hard. I battled back and I'm glad things went my way."
Sixth seed Caroline Wozniacki saw off Australian qualifier Ashleigh Barty 6-4 6-2.
The Dane could next meet world number one Karolina Pliskova, who was leading Italian qualifier Camila Giorgi 3-0 when play was suspended.
Fifth seed Elina Svitolina, who could become world number one if she wins the title, has yet to start her third round tie against Germany's Julia Goerges and could then also face the winner of another delayed match between American Sloane Stephens and Russian Ekaterina Makarova on Friday.