You may have seen it if you’re a tennis fan. The ad begins with a young boy of 10 or 11, sitting in a humble apartment watching Venus Williams on a tiny antique television. He’s interrupted by a man tapping him on his shoulder.“Hey Frances,” the man says, “What if a wall isn’t an obstacle, but an opportunity?”The apartment melts away and now the boy and the man — presumably a coach — joyfully hit beautiful looping groundstrokes against a wall. As they hit, the sweet-faced boy grows gradually older, finally melding into a regal, heavily muscled adult, his head crowned by a now-familiar headband as he delivers a sizzling ace and the crowd roars. It is Frances Tiafoe, one of the most popular and recognizable faces in men’s tennis, now ranked 10th in the world and considered a contender in the U.S. Open, which begins Monday.Of course the young Tiafoes in the ad were the product of a casting call, not the actual young Frances. But the producers did a good job finding someone who looked like the 11-year-old boy I met in 2009, when I spent a couple of months writing about the Junior Tennis Champions Center in College Park, Md., a then-obscure tennis training academy which had shockingly produced three boys in the world’s top 20 of junior tennis. I eventually accompanied their top two players, Denis Kudla and Mitchell Frank, to the French Open, where they competed in the junior championships.But here’s the relevant bit: During my reporting at the tennis center, I spent a day with a boy the coaches seemed to have a strange regard for. Kudla might actually make it to the pro tour, they said, adding: “But this kid is going to be better. This kid is special.”I was baffled. He appeared to be an ordinary 11-year-old, a ringer for the first kid in the ad — except instead of stylish new tennis duds he was wearing a well-worn Pikachu T-shirt. Frances was not especially big for his age, with no notable force of personality I could detect except an open and appealing disposition. I spent a morning in an attic above the tennis courts with him while he suffered through a geography class that was part of the in-house academic program. He wasn’t sullen, as so many kids would be, forced to focus on latitude and longitude with a strange adult looking over his shoulder. It was more a mild bemusement: “How did I end up here when I could be playing tennis?”After class I hit with him. He was really good for his age. But I noticed that after he hit the ball, he didn’t immediately bounce back into position for the next shot — a trademark of a serious player. And when I watched him play in a local tournament in a dingy sports bubble, he beat an older kid, but only by moon-balling him to death. I couldn’t see why the coaching staff was so high on him.A year later, I returned to the tennis center, and Frances, now 12, had replaced the moon ball with fearsome topspin groundstrokes that shot off the court and smacked into the back fence with a thud. When he was 15 — just four years after he left me so unimpressed — Tiafoe became the youngest player to win the Orange Bowl, the world’s premier 18-and-under tournament, which had previously crowned Bjorn Borg, John McEnroe, Ivan Lendl, Jim Courier, Roger Federer and Andy Roddick.When I delved into what it was, exactly, that the College Park pros had seen in Frances that I had missed, I discovered I had some expert company in my oversight.Kudla left College Park when he was 18 and became the first Junior Tennis Champions Center alumnus to break into the top 100 in men’s tennis, peaking in 2016 at No. 53 in the world. He knew better than most what combination of skill, dedication and gut-busting work that took.Early in his pro career, Kudla returned to the tennis center for a visit, a conquering hero. Frances was 13, still a few years away from winning his first junior titles. When he saw Frances play, he was more than a little skeptical. “He had that weird technique, weird forehand, I didn’t think his tennis I.Q. was that high,” Kudla said.He hit with Tiafoe and had the same sense of his potential that I did.“I just never thought that he had the discipline to be top 100 — not from a fitness point of view, but from a decision-making point of view,” Kudla said. “Decisions on the court are so important and take so much work, so much instruction, so much studying. I didn’t see him doing that.“But I was also basing that on the way I did it. I’m definitely more of an overthinker than he is. He’s a lot more natural, a lot more creative, a lot more God-given with his hands, so I was wrong about that as well. I was definitely wrong about a lot of things with him.”Tiafoe turned pro in 2016 and quickly became a fan favorite. He had an infectious gaptoothed grin and a moving back story: The impoverished son of refugees from the civil war in Sierra Leone, he had grown up in the tennis center, where his father was a janitor, sometimes sleeping on a massage table head to toe with his twin brother, Franklin, when his dad worked late. He also had a performative flair and winning disposition to go with his killer forehand. He was an enthusiastic and indiscriminate hugger at the postgame handshake who obviously loved being on the court and drove the crowd into a frenzy with gutsy shotmaking, fist pumps and biceps flexes.He rose to the top 100 at 19, broke the top 50 at 20, and at 21 broached the top 30. No longer the shy little boy, he was 6 feet 2 inches and built like a linebacker, with 135 m.p.h. serves and forehands not much slower. Even then, Kudla remained skeptical that Tiafoe had what it took to make the top 10, and from 2019 to 2021 Tiafoe seemed to feed those doubts. He had a propensity to get ahead in matches and then lose focus. He lost too often to lower-ranked opponents in the first round of too many tournaments.During this period I suggested to the tennis center chief executive, Ray Benton, that Tiafoe’s career might have peaked at age 21. No shame in that, I said. Getting into the top 30 of the brutally competitive pro tour is almost a miracle to begin with. There are about 1,800 professional players in the ranking system, but only roughly the top 100 can make much of a living from competitive play alone. Benton himself had once told me: “There are 11 Americans in the top 100. That basically means there are 11 jobs in the whole world of tennis for Americans. How bad are your odds there?”Maybe, I suggested, Frances had finally found his limit at a very rarefied altitude.Benton just smiled and said, “Nope.”Really? I asked. Just how high did he think Frances could go?“All the way to the top,” he said. “No. 1.”What about that kid Carlos Alcaraz? I said. He looks like he will be eating everyone else’s lunch for a couple decades. And who knows if Novak Djokovic’s deal with the devil has an expiration date.Benton shrugged. “OK, then, top 10, at least.”As if on cue last summer, Tiafoe began to hang on in matches in which he had jumped to a lead. He would switch into a higher gear and finish, against even some top 10 opponents. He made a thrilling, stadium-shaking run to the U.S. Open semifinals, barely losing to Alcaraz. Along with Taylor Fritz, he is one of two American men in the top 10 for the first time in more than a decade.Which left me where I began — mystified. How did Benton know then? And how did his coaches know at the beginning?At the tennis center in 2009, I watched as Vesa Ponkka, the director of tennis, and the coach Frank Salazar ran a horde of local children through drills cleverly disguised as games in a “Free Fun Festival” at the academy. Some kids twirled like ballerinas or flapped their arms like birds when instructed to run…