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.
He will now face unseeded Frenchman Arthur Fils, who beat Mensik’s compatriot Jiri Lehecka 6-3 6-3, for the chance to play in a fourth ATP final and his second in 2026, having won last month’s Auckland Open for a second career title.
World number one Carlos Alcaraz will meet defending champion Andrey Rublev in the other semi-final after both won their last-eight ties.