World number two Iga Swiatek is out of the Dubai Tennis Championships after a shock 6-3 6-3 quarter-final defeat by 17-year-old Mirra Andreeva.
The Russian teenager is the youngest-ever player to reach the last four of the tournament.
She was 3-1 down in the second set before reeling off five games in a row to beat Poland's Swiatek, a five-time Grand Slam winner, in one hour 36 minutes.
Andreeva set up a tie against either Kazakhstan's Elena Rybakina or the United States' Sofia Kenin later on Thursday.
"Honestly, I was really nervous before the match and we played in Cincinnati last year [which Swiatek won] and it was pretty intense," Andreeva said.