World number one Novak Djokovic underlined why he is favourite to win the ATP Finals with a commanding win over John Isner in their group opener.
The Serb, 31, was in devastating form as he easily dealt with the big serves of American Isner in a 6-4 6-3 victory.
World number 10 Isner, making his debut at the season-ending tournament, was broken in the fifth game of the first set and seventh of the second.
Djokovic then sealed the win on Isner's serve with a crosscourt backhand.
Earlier in the day, Alexander Zverev beat Marin Cilic in straight sets in the other match in the Gustavo Kuerten group.