Novak Djokovic feels Italian teenager Jannik Sinner leads the pack of `Next Gen` players with the potential of becoming a future world number one, the Serbian said after all but securing his year-end top ranking with a win in Vienna on Wednesday.

Djokovic saved four set points in the opener against Croatia`s Borna Coric to win 7-6(11), 6-3 to reach the third round of the Erste Bank Open in the Austrian capital.

The win meant that the 17-times Grand Slam winner could only be stopped from tying Pete Sampras` record of finishing as year end No.1 for the sixth time if Rafael Nadal accepts a wild card in competing in Sofia next month.

The 19-year-old Sinner won the Next Gen ATP Finals in 2019 and is currently at a career-high ranking of 43, having reached his maiden Grand Slam quarter final at this month`s French Open.

“I definitely see a lot of quality in the young players,” said Djokovic. “(Sinner) definitely possesses a game that is powerful and is with a lot of quality, and you can say he has the potential to be a top player of the world.

“Sinner is definitely, I would say, the leader of the guys younger than (Alexander) Zverev and (Stefanos) Tsitsipas, who I think by many experts` opinions the next `top` top player.”

German Zverev, aged 23, reached the U.S. Open final in New York and is a year older than Greek Tsitsipas and they have won the previous two editions of the season-ending ATP Finals, the biggest event in men`s tennis outside the Slams.

Djokovic felt the duo are already established players and would need to sustain their performances over a period to wrest the top ranking.

“Many things have to come together in a career and life of a tennis player in order for him to be able to find his best and maximise his potential and to thrive every single year,” Djokovic said.

“And to endure, because I think you have a much better chance to have a great Grand Slam or a great season. But can you endure for three, four, five, 10 years? Fifteen years?”