Novak Djokovic reached the final of the Astana Open after his opponent Daniil Medvedev withdrew because of injury on Saturday.
But just moments after Wimbledon champion Djokovic had taken the second set on a tie-break, Medvedev withdrew.
With the score at 4-6 7-6 (8-6), Medvedev called it quits, with Djokovic saying: "I'm shocked, really."
The Serb added: "He looked completely fine, but maybe the last seven eight, points I saw him move slower."
The 21-time Grand Slam champion will face Stefanos Tstisipas in Sunday's final as he bids for a 90th ATP title.
Tiafoe to face Fritz in Japan final
Frances Tiafoe will face fellow American Taylor Fritz in the final of the Japan Open in Tokyo.