TOKYO (Kyodo) -- Up-and-coming tennis player Rei Sakamoto capped an impressive year with his first ATP Challenger Tour title only three months after turning pro.

The big-serving 18-year-old, who stands 195 centimeters and has trained at IMG Academy in Florida since 2022, aims to take more steps in 2025 toward his goal of becoming the first Japanese man to win a Grand Slam singles title.

Sakamoto rallied for a 1-6, 6-3, 6-4 win over Germany's Christoph Negritu in the Dec. 1 final of the Yokkaichi Challenger, held near his hometown of Nagoya.

"It's a confidence boost, but I try not to be overconfident," the 2024 Australian Open junior singles champion said. "I'm starting to play persistently like a pro."

In his semifinal match in Yokkaichi, Sakamoto upset 21-year-old compatriot Shintaro Mochizuki, the 2019 Wimbledon junior singles champion.

"I believe Sakamoto will do better than (Kei) Nishikori if he can build up his physical strength," said Toshihisa Tsuchihashi, a Japan Tennis Association official in charge of player development.

Nishikori reached the final of the 2014 U.S. Open, only to lose to Croatia's Marin Cilic, at the age of 24 and rose as high as fourth in the ATP rankings before being slowed by a series of injuries in recent years.

When Sakamoto announced his decision to turn professional in September, he voiced his intention to become a Grand Slam champion at 24.

Asked what he wants most now, Sakamoto said, "More followers of my Instagram."

He currently has some 18,000 followers on the social media app.