Brazil's Joao Fonseca, 18, captures Next Gen ATP Finals title with Rafael Nadal watching on

The future is Joao! Eighteen-year-old Brazilian Joao Fonseca completed a perfect week at the Next Gen ATP Finals with a 2-4, 4-3(8), 4-0, 4-2 victory over American Learner Tien on Sunday, becoming the second-youngest champion in the seven-year history of the competition.

With Rafael Nadal watching on from the stands, eighth-seeded Fonseca bounced back from losing the first set to defeat Tien for the second time in five matches in Jeddah, and finish the eight-man competition for the world's best 20-and-under players at 5-0.

Fonseca had previously beaten Tien, the fifth seed and winner of three Challenger titles this year, in the junior US Open final in 2023, and staved off the American, whom he also beat in four sets in Jaddah's group stage, by turning around a key second set.

Already up a set, the 19-year-old had a set point in the second-set tiebreak to move ahead by two best-of-four-game sets to love, but failed to convert it. Two points later, Tien's backhand broke down, and he buried a first-ball backhand off Fonseca's return to knot the match at one set all.

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"I was really nervous before the match. I knew it was going to be so difficult," Fonseca said post-match. "I played a final against Learner in juniors [at the 2023 US Open] and I know the way he can play. He is such a nice guy and a great player, so I knew it was going to be difficult, mentally and physically. But I got my way through."

"Honestly, I don't know how I did it in the second set," he added. "I was just trying to keep my game strong on serve. I was not playing my best at the beginning, I was too nervous. But after the second set, I think the third set was another Joao. I was much more aggressive going for the shots and he got a little bit more tight. In the fourth set I just did my best and got the win."

For his undefeated week, Fonseca will take home a tournament-record $526,480 prize money, and the left-hander will start 2025 ranked No. 145 after starting 2024 outside the Top 700.