Top seed Belinda Bencic was made to battle hard against Viktorija Golubic to book her place in the semi-finals of the Rosmalen Grass Court Championships.
Bencic was pushed all the way by her Swiss compatriot on Friday, but the world number eight moved up a gear in the tie-breaks to win 7-6 (8-6) 7-6 (7-2).
The victory makes it three wins from three for Bencic since making her return from a back injury.
Belgian qualifier Elise Mertens saw her run at the tournament come to an end at the hands of third seen Kristina Mladenovic, who won 7-5 6-3 to keep her championship hopes alive.
Mladenovic, who is best known as a doubles player and recently won the French Open with Caroline Garcia, now faces Bencic for a place in the final as she chases a maiden WTA singles title.
Coco Vandeweghe made light work of Evgeniya Rodina, moving into the last four with a 6-2 6-2 win that was sealed in just under an hour.
Vandeweghe will face Madison Brengle in the second semi-final after her fellow American also came through the quarter-final stage beating Kateryna Kozlova 7-5 6-4.