World No. 2 Daniil Medvedev came from a set down to power past ATP Finals debutant Hubert Hurkacz 6-7 (5-7), 6-3, 6-4 and get his title defense off to a winning start in Turin on Sunday.
Olympic champion Alexander Zverev was also awarded a win in his opening match after Italian Matteo Berretini pulled out injured early in the second set with the German leading 7-6, 1-0.
Russian Medvedev, who won the U.S. Open title in September for his maiden Grand Slam crown, allowed his Polish opponent to take the early advantage in the season-ending event following a tight tiebreaker, but responded in style.