The storylines of five 2025 challengers including Justin Engel, Nicolai Budkov Kjaer, Joao Fonseca | ATP Tour

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Teenagers Engel, Budkov Kjaer, Fonseca are the storylines for five Challengers players in 2025

Germany’s Engel, 18, is the youngest Challenger champion this season

December 8, 2025

From teenage breakthroughs to the reigning NCAA champion’s arrival on the professional stage to his historic championship run in Africa, ATPTour.com looks back at the storylines of five Challenger players heading into the 2025 season.

German teenager Engel becomes youngest champion in 2025
Hamburg fans witnessed the rise of a new German star as Justin Engel captured his first ATP Challenger title in his hometown.

At 18 years and 25 days old, Engel became the youngest Challenger champion this season and the fifth youngest German champion in history. The #NextGenATP teenager defeated 18-year-old compatriot Federico Cina 7-5, 7-6(4) in the final, the youngest player in the championship since Mario Ancic beat Rafael Nadal in Hamburg in 2003. Engel became the first player born in 2007 to win an ATP Challenger title.

“Every championship is a big championship, especially my first challenger,” Engel said at the time. “Cinna is a great player and I knew before the game it was going to be a difficult game. This win makes the game even better and I’m really happy.”

Zheng goes from NCAA champion to three-time Challenger champion
College tennis players continue to perform well on the Challenger Tour, including Michael Cheng, who won the 2024 NCAA singles title representing Columbia University and successfully defended his title last month.

Due to his success in college, Zheng qualified for the ATP Next Gen Accelerator, a program designed to provide top players in the U.S. collegiate system with additional development pathways to earn direct access to select Challenger events. In August, Zheng made the most of one of his accelerator seats at Challenger Chicago, working his way into the winner’s circle with a world ranking of 416. Zheng then added to his title with back-to-back trophies in Columbus and Tiburon in September.

“It’s definitely a super helpful program,” the 21-year-old said of the accelerator program. “It gives players a lot of motivation to go to college and go down that path. You start your career like that… you get as good as I did in Chicago and then all of a sudden you’re ranked right there and can get yourself into the main game with the Challengers. I think it’s a great move.”

Michael Cheng wins the Tiburon Challenger. ” style=”width:100%;” src=”https://www.atptour.com/-/media/images/news/2025/10/06/15/26/zheng-tiburonch-2025.jpg”>
^{Michael Cheng won the Tiburon Challenge. Photo credit: Natalie King}

Koulibaly’s historic title in Ivory Coast
Eliakim Coulabili’s first Challenger title run couldn’t have been scripted better. His native Côte d’Ivoire hosted back-to-back events and became the 95th country to host an ATP Challenger Tour event – and it was in the capital Abidjan that Koulibaly achieved a very different result, ending one of the most memorable moments of his career.

Koulibaly’s free play brought plenty of cheers to his home fans after their first-round loss in Week 1. The Ivorian ended the title match with a three-set victory and fell to the ground in relief as the native stood up. Koulibaly became the first Ivorian player to win the Challenger League.

Looking back on his full journey, Koulibaly said: “Never stop believing, man. Never stop believing. I’m from fire. I’m from Africa. As an African, it’s difficult to be successful on the ATP Tour. You don’t see too many African players trying to compete because it’s difficult. But for me, it’s just discipline, never stop believing. It’s been a tough journey for me.”

#NextGenATP Budkov Kjaer completes historic season, joins Gasquet, Rune and Coria in records
Remember the name Nikolay Budkov Kjaer. The 19-year-old will compete in this month’s Next Generation ATP Finals hosted by PIF, where he is one of six players to win a season-leading four Challenger titles. The Norwegian becomes the fourth youngest player to achieve this feat, joining Richard Gasquet, Holger Rune and Guillermo Correa, all of whom have reached the top ten in the PIF ATP Rankings.

“You always want to believe in your ability to beat the top guys, and I always believed I was a very dangerous opponent,” Budkov Kjaer said after winning his first Challenger title in Glasgow in February. He was also crowned champion in Tampere, Astana and Mouyron-le-Captiv.

Fonseca and del Potro share history
Joao Fonseca has made history in the ATP Challenger Tour after a meteoric rise over the past 12 months since winning the Next Generation ATP Finals at PIF. Just 13 days after his victory in Jeddah, the Brazilian won the Canberra Challenge, joining Jannik Sinner as the only players to win the subsequent tournament after winning the 20-and-under event.

Then, at the ATP Challenger 175 event in Phoenix in March, Fonseca won his third trophy at the level and became the second youngest player from South America (behind Juan Martin del Potro) to achieve the feat. Fonseca also won the ATP 250 in Buenos Aires and the ATP 500 in Basel, becoming the fourth youngest player to win an ATP Tour event and an ATP Challenger event in the same season. He plays alongside Kei Nishikori and three members of the ATP No. 1 club. Carlos Alcaraz, Andy Roddick and Lleyton Hewitt are the five youngest players to achieve this feat.