COLLEGE PARK, Md. — An Aston Martin, a Bentley and a Jaguar are among the cars parked at the Tennis Center at College Park. Through the door of the private club one will find luxury locker rooms; 30 courts; a health club; and an office, about 120 square feet with one window, that was once a makeshift apartment the janitor called home.

From 1999 to 2010, its tenants were three members of the Tiafoe family: Constant and his twin boys, Francis and Franklin.

While Tiafoe, the center’s maintenance man, made his rounds, tending to the courts and emptying the trash bins, Francis would follow, occasionally drifting away to hit a few balls. The costs of elite tennis are prohibitive for many parents — the full-time junior program here is $27,500 a year — but Francis had ready and free access to the sport and some of the best coaches because of his father’s job.

From that unusual arrangement, a young tennis star was born. Today, Francis Tiafoe, 14, is the nation’s top-ranked boys player in his age group.

“It could be argued that Francis is the luckiest kid in the world,” Ray Benton, the tennis center’s chief executive, said. “It was pure serendipity. He didn’t pick tennis; tennis picked him.”

When the French Open begins May 27, analysts and fans will lament the state of men’s tennis in the United States. John Isner is the top-ranked American at No. 10, and he is hardly considered a formidable threat to win a Grand Slam tournament. The last American man to win a major was Andy Roddick, at the 2003 United States Open. If Francis continues his ascent, he could be the country’s next, best hope in the sport — a notion that would have been inconceivable to his parents when they immigrated from Sierra Leone in the early 1990s.

Tiafoe and his wife, Alphina, had twin boys in 1998, and two years later he took a job on the construction crew that was building the tennis facility.

“I worked harder than everybody else as I was the only black guy on the crew,” he said.

When the club was completed, Tiafoe was hired to do maintenance. Responsible for opening and closing the center, and everything in between that did not directly involve tennis, he often slept only three hours a night. His starting salary was $21,000 a year. When the staff told him he could stay in the spare office, he made it a home for him and the boys, who stayed at least five days a week. The rest of the time the children stayed with Alphina, who lived with relatives in a one-bedroom apartment in nearby Hyattsville.

“We didn’t have a certificate of occupancy, so I was really nervous about telling people he lived in a back room,” Benton said.

Alphina said she liked the arrangement because the center was a safe haven from her blighted neighborhood.

At first, no one at the center paid much attention to the boys. But the boys, especially Francis, paid attention to the action on the courts. Frank Salazar, one of the coaches, said that from the time Francis was 4 “he had a tennis racket in his hands.” For years, Francis would watch instructors give lessons to older boys.

“When we would get done training the bigger boys, he would roll the basket out there and try to serve by himself or play some mini-tennis with whoever had a few minutes,” Salazar said.

“Suddenly he started to get really good. He’s probably watched more tennis than all the kids here combined.”

When Francis was 8, Mikhail Kouznetsov was hired to coach at the club’s Junior Tennis Champions Center. He became a second father of sorts to the Tiafoe children. Alphina called him “a godsend and a miracle.”

“I would come in early, around 5, 6 a.m., and wake the boys up to play and feed them balls or whatever,” Kouznetsov said. “Me and my wife loved them, so we helped feed them, buy them shoes and when we needed to, we drove Francis to tournaments and paid his entrance fees out of our own pockets.”

Constant Tiafoe left his maintenance job at the center in 2010 and is unemployed. The family now lives in the apartment in Hyattsville.

But the boys remain immersed in tennis almost exclusively. Francis said he had no friends outside the center. His girlfriend, he said, is also a world-class player there.

The Tiafoe boys’ development was not always smooth. Franklin also exhibits impressive skills on the court, along with some petulance.

“You would know Franklin is playing because all you would hear is curse words ringing from somewhere in the courts,” said Ken Brody, who founded the Junior Tennis Champions Center in 1999. “Roger Federer was the quintessential hothead when he was a junior. They grow out of it.”

Schoolwork can be a struggle for Francis, and the fitness regimen and practice drills sometimes flustered him.

“I’d give him a C in gym glass,” said Frank Costello, the senior director of fitness. “There’s good days and bad days.”

But Francis’ results on the court have been so promising that shortcomings may be easy to dismiss. In January he won the boys’ singles title at an international tournament in Bolton, England. A week later, he won Les Petits As, a prestigious tournament in Tarbes, France, which attracts many of the world’s best young players.

He now has endorsement deals with Adidas and Wilson.

“I knew I was going to play pro tennis when I was 12,” Francis said.

“Tennis is my life.”

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