Novak Djokovic was knocked out of the Dubai Tennis Championships after losing 6-4 7-6 (7-4) to the Czech Republic's Jiri Vesely in the quarter-finals.
The tournament was the Serb's first of 2022 after he was not allowed to compete in the Australian Open because he is unvaccinated against Covid-19.
Djokovic is now set to lose his number one ranking to Daniil Medvedev.
Vesely told Amazon Prime: "I never thought I would really have a chance against Novak."
Vesely was broken when serving for the match before winning the second set tie-break to complete victory.
"It's an amazing feeling," he added after upsetting Djokovic.