Karolina Muchova defeated French Open champion Coco Gauff 6-3, 5-7, 6-3, marking a challenging start to Gauff's claycourt season. Mirra Andreeva eliminated four-time Roland Garros winner Iga Swiatek with a 3-6, 6-4, 6-3 victory in the Stuttgart Open quarter-finals.
Gauff, the world number three, committed numerous unforced errors against Muchova, a player she had previously dominated. Despite winning the second set, Gauff could not overcome Muchova's decisive break in the third.
Muchova, ranked 12th, described the match as a "battle" and expressed relief at managing the crucial breaks. She is set to face Elina Svitolina in the semi-finals.
In the other major upset, 18-year-old Mirra Andreeva overcame world number four Iga Swiatek. After Swiatek took the first set, Andreeva fought back, holding her nerve to force a decider and ultimately secure the win.
Swiatek acknowledged her performance was "not enough" despite seeing progress in her baseline game. Andreeva will advance to face either Elena Rybakina or Leylah Fernandez.