Garbine Muguruza and Petra Kvitova reached the semi-finals of the Aegon Classic following their wins on Friday.
The former French Open winner faced CoCo Vandeweghe, but the American was forced to retire with scores at 6-4, 4-6.
Vandeweghe injured her right ankle at the end of the second set and after just two points in the decider, it was clear she could not play through it.
"I know what it feels like to retire," Muguruza said during her on-court interview.
"It's very frustrating because she was playing a great match. It's sad for it to end like this. What can I say?"
Muguruza faces Ashleigh Barty in the semi-finals after the Australian advanced courtesy of another retirement, this time from Camila Giorgi after Barty was 5-2 up in the first set.
Meanwhile, fifth Kvitova eased past Kristina Mladenovic 6-4, 7-6(5) to set up a final four clash with Lucie Safarova, who battled past ninth seed Daria Gavrilova 6-7(4), 6-3, 7-6(5) in a hotly contest match.