15-year-old Catherine Bellis pulls off biggest upset of U.S. Open, seven months after winning Costa Rica tournament

Catherine Bellis, a 15-year-old from California, completed the biggest shock of the U.S. Open’s first round after knocking off No. 12 seed Dominika Cibulkova on Tuesday.

Bellis defeated the former Australian Open finalist 6-4, 4-6, 6-4 and even Bellis admitted afterwards, “I never thought I would come out on top winning.” But while this was Bellis’ biggest upset of the year, it wasn’t her first. The teen’s year got off to a spectacular start when she won the 2014 Copa del Café tournament in Costa Rica.

The Copa del Café is a junior circuit tournament played every January at the Costa Rica Country Club in Escazú. Past participants include tennis legends like Roger Federer, Bjorn Borg and Ivan Lendl.

At the 50th edition of the Copa del Café, a 14-year-old Bellis surprised top-seeded Czech player Marie Bouzkova to win the tournament. She’s carried that momentum into the rest of the year.

Bellis is the youngest girl to win a match at the U.S. Open since Anna Kournikova did it in 1996. Bellis, ranked 1,208th in the world, only qualified for the U.S. Open after winning the USTA girls’ 18s national championship. There, she was the youngest player to win the tournament since Lindsay Davenport in 1991.

She then recovered from a 3-1 deficit in the third set against Cibulkova to win her first Grand Slam match.

Catherine Bellis of the United States hugs coach Leo Azevedo in celebration after defeating No. 12 seed Dominika Cibulkova of Slovakia during their 2014 U.S. Open women's singles first round match in New York City. AFP

When Bellis won the Copa del Café in front of a few thousand fans, she told media that “I began a little nervous because I had never played before so many people, but luckily everything went well.”

Now Bellis has a much bigger audience — and a few more fans. Per the New York Daily News:

Afterward, it took several security guards and event workers to separate the crowd of autograph-seekers blocking Bellis’ path back to nearby Arthur Ashe Stadium. She stood in the hallway holding her cell phone, trying to process the wave of text messages flooding in. “I can’t even count,” she said, scrolling endlessly downward with her thumb. “It’s still going.”

Then the home-schooled youngster, who counts Kim Clijsters as her idol, held court with the media for almost 15 minutes while her father filmed with a home video camera from the auditorium seats.

“I’m feeling amazing. I’m still speechless,” Bellis said. “I’m still in shock from the match.”

Twelve U.S. women advanced to the second round of the New York City-based tournament, including No. 1 seed Serena Williams. Only three U.S. men advanced to the second round. The highest ranked U.S. player, No. 13 John Isner, is also a former Copa del Café participant. Isner beat compatriot Marcos Giron in straight sets in the first round.

Bellis will try to build on her stunning victory when she takes on No. 48 seed Zarina Diyas of Kazakhstan on Thursday.