Second seed Dominika Cibulkova was a quarterfinal loser, while Romanian Simona Halep remained perfect on grass in 2013 at the $235,000 Topshelf Open, a final Wimbledon tune-up.
Spanish qualifier Garbine Muguruza took down the Slovakian Cibulkova 6-4, 6-4, while Halep leveled lucky loser and fellow non-seed Lesia Tsurenko of Ukraine 6-3, 6-1 on Day 5 at Autotron Rosmalen.
The 21-year-old Halep is fresh off her first-ever WTA title in Germany last week and now 8-0 on grass this year.
Also on Thursday, third-seeded Spaniard Carla Suarez Navarro overcame Bulgarian grass-court specialist Tsvetana Pironkova 2-6, 6-4, 6-4 and fourth- seeded Belgian Kirsten Flipkens doused seventh-seeded Pole Urszula Radwanska 6-4, 6-4. Radwanska was last year's Den Bosch runner-up to Russia's Nadia Petrova.
Friday's semifinals will pit Suarez Navarro against Halep and Flipkens versus Muguruza.
This week's champion will earn $43,000.