Jannik Sinner began his title defence of the Sofia Open on Thursday with a 6-2, 7-6(3) win over qualifier Egor Gerasimov.
Sinner is another player chasing points to make the ATP finals to Turin next month.
The young Italian had as slow start to 2021 but has bounced back by winning 10 of his previous 13 matches, including a title in Washington in August.
“I think this year what I have done was good, with some ups and downs,” Sinner said.
“Every week when I play it’s trying to understand something new, trying to learn something new.”