Teenager Belinda Bencic of Switzerland will face veteran Jelena Jankovic of Serbia in the semifinals of the Topshelf Open after saving three match points in a 7-6 (4), 6-7 (4), 7-5 win against seventh-seeded Kristina Mladenovic of France on Friday.
The 18-year-old Bencic had match point at 6-5 in the second set, only for Mladenovic to fight back in a contest lasting nearly three hours. Mladenovic hit 16 aces and had three match points at 5-3 in the decider before Bencic surged back.
"She was serving so well, but in my head I was prepared for it," Bencic said. "She served so many aces on important points and it's difficult, because it puts a lot more pressure on your serve, but I was ready for it. It was just an amazing match."
The 30-year-old Jankovic had it easier, beating German Annika Beck 6-4, 6-1.
Fifth-seeded Camila Giorgi of Italy also saved three match points in a 4-6, 6-3, 7-6 (9) win against Kazakhstan's Yaroslava Shvedova.
Giorgi next faces Dutchwoman Kiki Bertens, who beat third-seeded American Coco Vandeweghe — the defending champion — 6-4, 6-1.
Dutch fans will be hoping for a home double, with Robin Haase reaching the men's semifinals with a 6-7 (4), 6-4, 7-6 (3) win over big-serving Ivo Karlovic — who had 24 aces.
Bidding to become the first Dutch champion here since Sjeng Schalken in 2003, Haase next faces qualifier Nicolas Mahut, who downed sixth-seeded Adrian Mannarino 6-1, 6-3 in an all-French match.
Second-seeded David Goffin of Belgium also advanced to the last four after rallying to beat Ukrainian Illya Marchenko 4-6, 7-6 (3), 6-2.
He next plays either Gilles Muller of Luxembourg or Marius Copil of Romania, who were playing their quarterfinal later Friday.