Novak suffered a three set loss on Tuesday evening at the Nitto ATP Finals.
Top seed and defending champion Novak Djokovic failed in attempt to score his second win in Green Group at the 2023 season finale in Turin, as he was defeated by no.4 seed Jannik Sinner 5-7, 7-6 (5), 6-7 (2) in three hours and eighth minutes at Pala Alpitour.
Sinner produced one of the greatest performances of his career. This was his first victory against Djokovic in their four H2H meetings.
Novak broke once from three opportunities, while the Italian converted two of his three break point chances.
Match statistics: aces (19-15), double faults (1-2), winners (42-39), unforced errors (26-33), total points won (109-109).
Novak will look to book his place in the last four when he meets alternate Hubert Hurkacz in the final round-robin match on Thursday (14:30 CET). The Pole will replace injured Stefanos Tsitsipas.
Jannik Sinner, who improved to 2-0 this week in Turin, will play against Holger Rune.
Djokovic is bidding to triumph at the year-ending tournament for a record seventh time.