Jannik Sinner lifts his fourth ATP Challenger Tour trophy of 2019 in Ortisei.

Jannik Sinner celebrates his fourth Challenger title of 2019 in Ortisei.

Jannik Sinner advances to the quarter-finals at the ATP Challenger Tour stop in Ortisei.

Jannik Sinner is back in action at the Ortisei Challenger.

Jannik Sinner is back in action at the Ortisei Challenger.

Jannik Sinner, the 18-year-old who is the youngest player in the Top 100, wins the Next Gen ATP Finals.

Jannik Sinner was ranked outside the Top 500 to start 2019. On Sunday, he won the Next Gen ATP Finals title.

Jannik Sinner becomes the first Italian to win the Next Gen ATP Finals in Milan.

At No. 95 in the ATP Rankings, Jannik Sinner is the lowest-ranked player to win the Next Gen ATP Finals.

Jannik Sinner, who watched the 2018 Next Gen ATP Finals from the stands, triumphs in Milan.

Jannik Sinner was all smiles ahead of the Next Gen ATP Finals title match.

Alex de Minaur and Jannik Sinner got their hands on the trophy before battling in the Next Gen ATP Finals title match.

Jannik Sinner gives his coach, Riccardo Piatti, an incredible birthday present by reaching the championship match at the Next Gen ATP Finals.

Jannik Sinner wins 12 of the last 17 games to defeat Miomir Kecmanovic at the Next Gen ATP Finals.

Jannik Sinner's 56-minute win over Mikael Ymer is the second-fastest in tournament history.

Jannik Sinner's 56-minute win over Mikael Ymer is the second-fastest in tournament history.

Jannik Sinner records the most dominant scoreline in tournament history with his win over Mikael Ymer.

Jannik Sinner becomes the first Italian to win a match at the Next Gen ATP Finals.

Jannik Sinner was all smiles during his practice at the Next Gen ATP Finals.

The third edition of the Next Gen ATP Finals will take place from 5-9 November at Allianz Cloud, Milan.

(L to R): Mikael Ymer, Jannik Sinner, Alejandro Davidovich Fokina, Frances Tiafoe, Ugo Humbert, Miomir Kecmanovic and Casper Ruud attend the launch for the 2019 Next Gen ATP Finals.

(Clockwise from centre): Ugo Humbert, Frances Tiafoe, Miomir Kecmanovic, Mikael Ymer, Jannik Sinner and Alejandro Davidovich Fokina pose for a group selfie during the 2019 Next Gen ATP Finals launch.

Local favourite Jannik Sinner will be in Group B for the 2019 Next Gen ATP Finals.

(L to R): Casper Ruud, Mikael Ymer, Miomir Kecmanovic, Jannik Sinner, Frances Tiafoe, Ugo Humbert and Alejandro Davidovich Fokina enjoyed this year's launch party at the Lavazza Flagship Store.

(L to R): Mikael Ymer, Jannik Sinner, Alejandro Davidovich Fokina, Frances Tiafoe, Ugo Humbert, Miomir Kecmanovic and Casper Ruud attend the draw party for the 2019 Next Gen ATP Finals.