Casper Ruud opened his ATP Finals campaign with a 7-6 (7-4) 6-4 triumph over Felix Auger-Aliassime in Turin.
The victory put Ruud top of the Green Group, with the pool's two other players, Rafael Nadal and Taylor Fritz, set to face off later on Sunday.
A tight first set saw each game go to serve as it went all the way to a tie-break, with Ruud – this year's beaten US Open finalist – finding a crucial break at 3-2 up, giving him the momentum to nose ahead.
They continued to be closely matched in the second set too, though Ruud again managed to break Auger-Aliassime at a critical juncture in the match.
With the set tied at three apiece, ATP Finals debutant Auger-Aliassime double-faulted at 40-15 down on his own serve to put Ruud within two games of victory.
The world number four took full advantage, who is making his second appearance in the season-ending tournament, kicking on to secure a straight-sets success without offering a single break point to begin his tournament in impressive fashion.
Ruud - 5/1
Auger-Aliassime - 14/3
Ruud - 19/5
Auger-Aliassime - 30/9
BREAK POINTS WON
Ruud - 1/1
Auger-Aliassime - 0/0