Teenager Mirra Andreeva upset second seed Iga Swiatek 6-3, 6-3, to reach the last four of the Dubai Championships Thursday.
The 17-year-old Russian came from a break down in the second set to win in one hour and 36 minutes and continue the cull of the leading seeds in Dubai.
Andreeva, who also reached the semi-finals at Roland Garros last year, became the youngest semi-finalist in the Dubai tournament's 25-year history.
Swiatek, a 23-year-old Pole, had reached at least the last four of her three previous tournaments this season, but was clumsy at the net and shaky on key points.
The five-time Grand Slam winner failed to convert seven break points before finally taking her opponent's serve for a 3-1 lead in the second set but Andreeva responded by taking the next five games.
Swiatek joins third seed Coco Gauff, out in her opening match, world No.1 Aryna Sabalenka, fourth-seeded defending champion Jasmine Paolini and fifth seed Jessica Pegula to be knocked out.
Sixth seed Elena Rybakina, who faces unseeded Sofia Kenin later, is the highest ranked player still standing. Andreeva will face the winner of that match in the semi-finals.
