Jannik Sinner began his ATP Finals title defence by sweeping aside a physically hampered Felix Auger-Aliassime in front of a passionate Turin crowd.
Italian second seed Sinner was imperious on serve in a 7-5 6-1 win over the Canadian.
Eighth seed Auger-Aliassime was brilliantly aggressive in a competitive first set and was two points away from forcing a tie-break before tweaking his left calf.
The 25-year-old called for the physiotherapist twice in the second set, where he won just one game.
Victory puts Sinner top of the Bjorn Borg Group as he bids to secure the year-end world number one ranking.