Platoons of ballboys and ballgirls sprinted back and forth to limber up for the job in store. A groundskeeper filled the courts’ empty water coolers, while an announcer tested the microphone on nearby Suzanne Lenglen Stadium.

Apart from the 18-year-old across the net and an elderly man looking on through a wrought-iron fence, it was as if Roland Garros was Francis Tiafoe’s private domain Saturday when he and fellow American Noah Rubin launched into their 8 a.m. practice session well before the gates opened.

If Tiafoe’s tennis future unfolds as it does in his dreams, the 16-year-old Prince George’s County native may one day rule the sport’s lone clay-court Grand Slam event. For now, he is one of the game’s bright hopefuls — the teen shouldering the greatest expectation when he makes his French Open debut Sunday as the junior draw’s No. 1 seed.

“It was an unbelievable feeling, practicing on the same court all the other pros do,” said Tiafoe, whose introduction to tennis predates his memory. He and his twin, Franklin, spent most of their days and many nights at the Junior Tennis Champions Center in College Park, where his father was a maintenance worker.

Tiafoe was 6 when he told his father he planned on becoming a champion tennis player. He has devoted the decade since to that goal, developing a particular love of clay-court tennis and the patience and tenacity it requires.

Francis Tafoe, 16, shown earlier this year, will make his French Open debut Sunday in the first round of the junior tournament. (Jahi Chikwendiu/The Washington Post)

As he grew up, he often dreamed of competing at the French Open. At the time, he didn’t realize there was such a thing as the French Open junior tournament; he thought he would have to become a bona fide pro ranked among the top 100 to get a chance.

That chance came Saturday, when he stepped onto one of the Roland Garros courts for the first time.

“Words can’t explain how happy I was,” Tiafoe said. “But I had to get over it quick; I came here to do my best.”

Tiafoe has trained on clay at the JTCC for years. But there is a singular quality to European red clay, which is why Tiafoe and Frank Salazar, the center’s senior director of high performance, left Washington for Spain on May 15.

There, Tiafoe entered a lower-rung pro tournament, where he won two matches before falling to a 23-year-old Belgian in three sets. From there, he went to Barcelona Total Tennis, an academy co-founded by Francis Roig, a longtime hitting partner of eight-time French Open champion Rafael Nadal.

Tiafoe has always been quick and agile on court. But to excel on clay, Salazar explains, players must move efficiently on court, using their legs to load more power and unleash it on the ball. With Roig and Jose Higueras, Tiafoe worked on that and other nuances of clay-court tennis, such as the art of sliding and timing shots.

“Sliding and hitting is really fun on clay,” said Tiafoe, rare among Americans for his affinity for the surface. “The points are longer. It’s more physical. And it’s easier on the body, as well.”

In addition to the singular “look” of its red clay, the French Open stands apart as the smallest, most intimate Grand Slam. With no provision for lights or retractable roof on its main court, it’s the only major that halts play at dusk — even if that means suspending proceedings in the fifth set with the score a nerve-frayed 7-7, as it did in Saturday’s third-round tussle between Andy Murray and Philipp Kohlschreiber.

And instead of LaGuardia-bound airplanes, the signature sound of the U.S. Open, the French Open is set to a soundtrack of chirping birds and chants of “Allez!” rendered in song.

Tiafoe’s first Saturday on the Roland Garros grounds was a busy one. It started with the two-hour practice on Court No. 15, included a visit to the Wilson store to get new grips and extra string for his rackets and ended at a banquet for the world’s top 18-and-under players, the 64 girls and 64 boys who will vie for the French Open junior title. Along the way, Tiafoe squeezed in a “selfie” with 14th-ranked Jo-Wilfried Tsonga of France.

He will open play Sunday against a lesser known Frenchman, 17-year-old wild-card Clement Larriere.

While Tiafoe’s French Open junior debut realizes a personal quest, it’s an open question what a victory — or, for that matter, a first-round defeat — would signify.

In some cases, winning junior Grand Slams foreshadows greatness. Sweden’s Stefan Edberg swept all four junior Grand Slams in 1983 and by 1990 was No. 1 in the world.

In other cases, hoisting a junior slam trophy ends up the high-water mark of tennis careers that sputtered.

Former pro Justin Gimelstob looks back on his own dominance of the junior ranks as a detriment. He was the country’s No. 1 player in the 12, 14, 16 and 18 age groups but peaked at No. 63 as a pro.

“I actually think my consistent success as a junior was a real negative to my career,” said Gimelstob, 37. “It created a cycle where the winning was so important. Even though I tried to work on developing my game, it created almost a self-fulfilling prophecy of winning being more important than the overall process.”