PARIS -- Stefanos Tsitsipas qualified for the ATP finals by beating Alexander Zverev 7-6 (2), 6-4 in the third round of the Paris Masters on Thursday, and top seed Novak Djokovic extended his winning streak to 15 matches.
Jannik Sinner, meanwhile, pulled out of the Paris Masters because of some questionable scheduling.
The seventh-seeded Tsitsipas earned his first win over a top 10 player this season, hitting 37 winners to 28 for Zverev.
"What a great relief to finally get that spot. I've been working extremely hard the whole year to be in Turin," Tsitsipas said. "I'm thrilled to be playing good tennis."
The Greek took a 3-0 lead but failed to serve out the first set at 5-3 by sending a backhand into the net.
In the tiebreaker, Tsitsipas capitalized on two consecutive forehand errors from Zverev to lead 5-2 before taking the first set with an ace.
Tsitsipas broke Zverev in the opening game of the second set and clinched the victory with his 10th ace.
Zverev can still qualify for the ATP finals but now depends on the results of other players.
Alex de Minaur and Hubert Hurkacz stayed in contention for the two remaining spots at the eight-man tournament that will be played in Turin from Nov. 12-19.
Before the Paris Masters, Djokovic, Carlos Alcaraz, Daniil Medvedev, Sinner and Andrey Rublev had already qualified for the ATP finals.
Djokovic did enough on Thursday to widen the gap with Alcaraz in the race for the year-end No. 1 rankings with a 4-6, 7-6 (2), 6-4 win over Tallon Griekspoor.
"I think he deserved more the victory today," Djokovic said of Griekspoor. "I started well but I felt poorly afterward. No injury, just a stomach virus in the past two or three days."
Djokovic raced to a 4-1 lead only to experience a sudden dip in form, dropping serve twice to lose the first set.
The six-time winner of the event served three double-faults in a poor ninth game and looked almost uninterested and barely played the points when Griekspoor was serving for the set.
The Serbian player called for a physician after the end of the opening set and appeared to take some medicine.
Djokovic saved two break points at 4-4 in the second set before taking a 5-0 lead in the tiebreaker and holding serve to level the match. He then broke in the fifth game of the final set only to drop serve with a double-fault at 4-3.
But Griekspoor made more errors and netted a backhand in the next game to allow Djokovic to serve for the match.
Djokovic converted his first match point when Griekspoor sent a backhand return wide.
Djokovic will meet Holger Rune or Daniel Altmaier in the quarterfinals.
De Minaur, who got a walkover into the quarterfinals after the fourth-seeded Sinner withdrew, will next play the fifth-seeded Rublev, who ousted qualifier Botic Van de Zandschulp 6-3, 6-3.
The 11th-seeded Hurkacz beat Francisco Cerundolo 6-4, 6-3 to next face Grigor Dimitrov, who cruised past Alexander Bublik 6-2, 6-2.
Karen Khachanov, who won the tournament in 2018, rallied to beat qualifier Roman Safiullin 4-6, 6-4, 6-2 to set up a quarterfinal match against Tsitsipas.