Jakub Mensik prevented Jannik Sinner from reaching another final as he knocked the world number two out of the Qatar Open quarter-finals.
The sixth seed from the Czech Republic edged the first set and, although Sinner levelled, 20-year-old Mensik took the decider to win 7-6 (7-3) 2-6 6-3.
That ended a run of 22 wins from 23 matches for Sinner, with his only defeat coming against Novak Djokovic in the Australian Open semi-finals last month.
The 24-year-old Italian reached 10 finals in 2025, winning the Australian Open and Wimbledon titles, but was upset by world number 16 Mensik in Thursday's first meeting in Doha.