World number one Simona Halep lost her first match at the Madrid Open in three years as sixth seed Karolina Pliskova continued her fine form.
Romania's Halep, who won the 2016 and 2017 titles, suffered her first defeat in 15 matches in the Spanish capital.
Pliskova produced a stellar performance to win 6-4 6-3, extending her winning run on clay to nine matches.
The Czech will face two-time Wimbledon champion Petra Kvitova or Russia's Daria Kasatkina in the semi-final.
French seventh seed Caroline Garcia reached the last four with a 6-2 6-3 win over Spain's Carla Suarez Navarro.