Top-seeded Simona Halep lost 2-6, 6-0, 7-6 (4) Friday in a back-and-forth match against Krisytina Mladenovic of France in the quarterfinals of the Aegon Classic.
Mladenovic was outplayed in the first set but then won the second in only 20 minutes as Halep imploded with five double-faults. She failed to serve out the match at 5-3 in the third, but clinched the tiebreaker when Halep netted a backhand.
It was Mladenovic's third upset of the week at the grass-court tournament, having previously ousted No. 5 Eugenie Bouchard, last year's Wimbledon runner-up, and No. 10 Barbora Strycova.
She will next play sixth-seeded Karolina Pliskova of the Czech Republic, who beat third-seeded Carla Suarez Navarro of Spain 6-2, 6-2.
The other semi-final will be an all-German match between Sabine Lisicki and Angelique Kerber.
Lisicki beat Daniela Hantuchova by 7-6 (2), 6-2, while Kerber ousted Katerina Siniakova 6-2, 6-4.