15-Year-Old American Phenom CiCi Bellis Has Left The Tennis World Speechless

On Tuesday, 15-year-old Catherine "CiCi" Bellis became the youngest girl since 1996 to win a main-draw match at the U.S. Open.

She came into the match ranked 1,208th in the world.

The upset may have stunned her competitor, 12th-seeded Dominika Cibulkova, and other tennis fans, but Bellis' former coach Michael Jessup knew from an even younger age that the American player was going to become a forced to be reckoned with.

"Even back [when she was nine] you could tell she was going to be a superstar," Jessup, who coached Bellis from age 9 to 11, told John Branch of The New York Times. "I've coached a lot of really good players, but she stood out, with her spunk, her spark. She didn't see pressure. She saw a challenge. She saw it as fun."

Bellis won the USTA Girls' 18s Nationals in early August, which earned her an automatic spot in the U.S. Open. Anna Kournikova was previously the youngest person to win a U.S. Open main-draw, also at age 15.

Bellis, who beat Cibulkova 6-1, 4-6, 6-4 in the first round, shocked commentators with her performance. According to Bruce Jenkins at SFGate, Chris Evert, who made it to the semifinals of the U.S. Open at age 16 in 1971, said on ESPN: "She has charisma and composure. She's not a big girl, but she has a big game for somebody that young, with great feel for her shots. The way she reacted to the pressure - she's out there loving every minute of it. No intimidation whatsoever."

After defeating Cibulkova, the teenager ran over to hug coach Leo Azevedo. Even Bellis was surprised by her win.

"I went into the match thinking it was going to be such a great experience, but I never thought I would come out on top winning," she told the crowed afterward.

U.S. Tennis Association national coach Richard Ashby, who has coached 12 and 13-year-old players told The Times: "She has a weapon in her forehand." In the photo below, the tennis star is seen using her powerful forehand against Great Britain's Maia Lumsden at Wimbledon on July 1, 2014.

Bellis also has a strong backhand. Here she is against Australia's Kimberly Birrell at the French Open on June 1, 2014 in Paris, France.

Cibulkova is a legitimate top-15 player. She reached the finals of the Australian Open this year, and has four career WTA titles.

Bellis is set to to play Zarina Diyas of Kazakhstan, who's currently ranked 48th in the world, later on Thursday.