After beating 22-time grand slam champion Rafael Nadal to reach the U.S. Open quarterfinal last Monday, Frances Tiafoe threw his racket on the floor and covered his face in bewilderment.

It felt like a seminal moment in the 24-year-old American’s career, a culmination of hard work and raw talent which has long been heralded as the potential future of men’s tennis in the country.

Now, with Tiafoe reaching the semifinals by beating Andrey Rublev in straight sets last Wednesday 7-6 7-6 6-4, he has recorded the best grand slam result of his career, the achievement made all the more impressive given his humble beginnings.

The crowd at Arthur Ashe Stadium delighted in the play of Tiafoe, the first Black American man to reach a U.S. Open semifinal since Ashe in 1972. And in a match where he didn’t lose a service game to the world No. 11, he couldn’t let them down.

In an on-court interview after the match, Tiafoe said, “I feel so at home at courts like this. This court is unbelievable. You guys get so far behind me; you know I want to play and want to give it my best. I always find a way somehow on this court. I always try to play great tennis, and I have been.”

Tiafoe’s route into tennis has been in no way traditional. His parents met in the U.S. after leaving Sierra Leone and had twins together, Franklin and Frances. Their father, Constant Tiafoe, started working at the Junior Tennis Champions Center in Washington, D.C., back in 1999 and eventually moved into one of its vacant storage rooms while working around the clock.

His two boys sometimes stayed with him, sleeping on a massage table, while their mother worked night shifts as a nurse. The unusual gateway into the sport allowed Tiafoe to start developing his skills, and, after beginning to train at the facility, he didn’t look back.

In 2015, he told CNN Sport, “Obviously, I wasn’t the wealthy kid or wasn’t having all the new stuff or whatever. But I was just living life. I could play tennis for free, the sport I loved,” adding that he wouldn’t change his upbringing for the world.

His coach, Wayne Ferreira, said Tiafoe’s story is movie material, but he must first win the U.S. Open or another grand slam event. He said, “You only get movies if you do well. But his story is very unique, and it’s a great story. And he’s very humbled. He’s a very, very, very nice individual: very great heart and kind. You’ve got to love him. He’s truly special.”

Make no mistake, though. This is no overnight success story. It’s a product of thousands of hours of work and a mentality that won’t take no for an answer. However, while the weight of a nation rests on his shoulders, Tiafoe has always just focused on making his parents proud. He says he didn’t want to let them down or take his opportunities for granted.