Of the five Americans in the top 50 of the men's singles rankings, 20-year-old College Park native Frances Tiafoe is easily the youngest and, perhaps, also the most exciting.

The son of immigrants from Sierra Leone, Tiafoe is the 45th-ranked men's tennis player in the world. The ranking — the highest of Tiafoe's career — is thanks in part to his third-round run at Wimbledon earlier this month, the first time he's reached the third round of a major.

"It was a great week. I learned a lot," Tiafoe said of his time in London. "I can beat quality players. Every day is a learning process, just keep working at it."

Tiafoe's star has risen significantly since he shared a spare room with his twin brother at the Junior Tennis Champions Center in College Park, where his father was a maintenance worker.

Tiafoe's father left war-torn Sierra Leone for London in the late 1980s before settling in Maryland in the early '90s, hoping to create a better life for his children. Tiafoe began playing tennis at an early age, getting free lessons at the center where his father worked. He hasn't put the racket down since.

Tiafoe began his second season with the Washington Kastles of the World TeamTennis league this week, winning a super tiebreak Monday to move them to 2-0 on the year. He also played with the Kastles last summer, but the six-time WTT champions suffered an uncharacteristically poor season, finishing with a 4-10 record.

The 20-year-old said he was excited to return to Washington for another season and hopes to bring more success to a team that once won 34 straight games and has featured prominent tennis stars like Serena and Venus Williams, Nick Kyrgios and reigning US Open champion Sloane Stephens.

"There's not a better team to play for," Tiafoe said. "Hopefully this year we get some more wins."

Kastles coach Murphy Jensen said he will measure Tiafoe and the other players less by their performance on the scoreboard, but instead by their enthusiasm, intensity and effort.

"These guys are professionals. They know what they're doing," Jensen said. "If we're fighting like crazy and looking out for the person to our right and left, we'll be okay."

Tiafoe won a number of high-level junior titles including the Les Petits As in France and was as high as No. 2 in the junior rankings. In 2013, at age 15, he won the Orange Bowl, a prestigious junior tennis tournament previously won by stars such as Andy Roddick and Roger Federer. Tiafoe was the youngest player ever to win the event.

Tiafoe also made headlines in August 2017 when he pushed Federer — a 20-time Grand Slam winner — to a fifth set in the opening round of the 2017 US Open before losing a tight final set.

In February, Tiafoe won the Delray Beach Open to earn his first career ATP title. Along the way, he defeated his idol Juan Martín del Potro — now the No. 4 player in the world — to become the youngest American to win an ATP title since Roddick in 2002.

Playing WTT matches for the Kastles is much different than playing tennis on tour because of the increased speed of the game, Tiafoe said, adding that the best thing about playing for the team is he gets to be close to where he grew up.

By joining the Kastles and playing in the Citi Open in Washington later this month, Tiafoe maximizes his time in familiar surroundings during the extremely travel intensive schedule of a tennis player.

"Well, I'm home," Tiafoe said. "You don't find yourself being able to play home that much. You look up and you know pretty much everyone in the crowd. … I can't complain."