World number one Simona Halep suffered a surprise defeat at the Stuttgart Open as opponent Coco Vandeweghe reached her first WTA Tour semi-final on clay.
Romania's Halep, who will still retain her ranking, lost 6-4 6-1 to the 26-year-old American.
Vandeweghe lost to Halep in her only previous clay court quarter-final, but was untroubled in a comfortable display on her least favoured surface.
The world number 16 will play Elina Svitolina or Caroline Garcia next.