For 16-year-old tennis prodigy Francis Tiafoe, it was a humiliating loss that changed everything.

Tiafoe was just 6 when he told his father that he wanted to be the greatest player ever to come from College Park’s Junior Tennis Champions Center, where Francis Sr., an immigrant from the West African nation of Sierra Leone, was working as a maintenance man.

Last year, after devoting nine years to that goal, Tiafoe confronted the harsh reality that he wasn’t training hard enough. The lesson took just 45 minutes. And it came in the most public, painful fashion: a 6-0, 6-2 pummeling in the 2013 Junior U.S Open Championship.

Not ranked high enough for a spot in the 64-player draw, which is open to the world’s top 18-and-under boys, Tiafoe was forced to win two qualifying matches to earn a place in his first Junior Grand Slam. But after earning his spot the hard way, he fell flat in his first-round match, steamrolled by 16-year-old Quentin Halys of France.

Looking back, Tiafoe says, that loss was the turning point that jump-started his surge up the junior rankings and has landed him as the country’s top-ranked junior boy and the No. 1 seed in the Junior French Open Championship June 1-7 in Paris.

“Right after the U.S. Open, I took a couple days off, slowed down and thought about what I was doing with my tennis,” Tiafoe says. “I had been playing a long time, but I wasn’t consistent. One week I’d try hard in the morning but not in the afternoon. And without consistency, it’s tough to get better. You’re just kind of playing off talent.”

So Tiafoe, who once used to sleep with his twin brother on a tennis center massage table when their father was living there, started spending more time in the gym. He started putting more effort into his practices, running after every ball, pretending that the lines didn’t count. And when his legs started tiring, he knew it was time to push harder.

“It changed everything,” recalls Vesa Ponkka, the JTCC’s director of tennis, of Tiafoe’s defeat at the Junior U.S. Open. “He got humiliated in front of everybody, because everybody who was anybody in tennis was there watching. He got humiliated, and he didn’t like how it felt.”

Loss on that scale, particularly under a white-hot spotlight, tends to affect highly touted juniors one of two ways, according to Ponkka. They undermine confidence, or they steel resolve. In Tiafoe’s case, it did the latter.

“He totally turned the tables around in six months,” Ponkka said. “If you get humiliated at the U.S. Open in New York, a lot of players would shrink. He expanded. He was mad about it. That’s the sign of a champion.”

In December, the Prince George’s County-born teen became the youngest player to win the Orange Bowl, the most prestigious international title for 18-and-under boys, achieving the feat at 15 — more quickly than even Roger Federer, John McEnroe or Bjorn Borg managed.

Tiafoe is now the No. 2 junior in the world, behind Germany’s Alexander Zverev, 17. With Zverev skipping the Junior French Open, Tiafoe has been installed as the No. 1 seed.

Seeded fourth is Halys, the top junior in France and the player who handed Tiafoe that pivotal defeat in New York eight months ago.