Coco Vandeweghe saved seven match points and needed five to edge out Alison Riske in a tense Rosmalen Grass Court Championships quarter-final.
In a dramatic match that lasted just shy of three hours, it was top seed and two-time champion Vandeweghe who came out on top 7-6 (8-6) 3-6 7-6 (14-12).
The opening set saw six breaks of serve and five set points go begging for Vandeweghe before she finally wrapped up the tie-break, but Riske was more composed when she hit back to force a decider.
Vandeweghe missed three chances to claim the first break of the third set, all of which would have given her the win, but Riske was unable to punish the world number 16.
Her semi-final opponent will be Aleksandra Krunic, while Kirsten Flipkens – who beat Kiki Bertens and Aryna Sabalenka on Friday – and Viktoria Kuzmova will contest the other last-four encounter.
Ashleigh Barty remains on course for a second WTA Tour title at the Nottingham Open after breezing past Katie Boulter 6-0 6-2.
The top seed will meet Indian Wells winner Naomi Osaka, a 6-4 6-1 winner against Mihaela Buzarnescu, in the semi-final, with defending champion Donna Vekic up against Johanna Konta.