Novak Djokovic, world number one, on Thursday, beat Alexnder Zverez 6-4 6-1, to reach the semis of the ATP Final in London.
The Serbian became the first player to reach the final of the tournament after the clinical win over Zverez and a favourable result in the other group’s match.
The 31-year-old, who is chasing a first ATP Finals title since 2015, qualified for the last four when Marin Cilic beat America’s John Isner later.
“I don’t think it was breathtaking tennis but a win is a win,” he said.
“I played well midway through the second set and started to swing through the ball.
“I had not served that well but he made a lot of unforced errors which helped me to win.”
It was a double-fault from the German that handed Djokovic the first set. His total of 33 unforced errors contributed to his downfall.
He himself later imply that fatigue had played a part in his defeat, also saying the length of the tennis season was “ridiculous”.
Djokovic will play Cilic in an inconsequential final round-robin match on Friday, while Zverev faces Isner.