CiCi Bellis, at 15 the darling of the first week of the U.S. Open, loves the big crowds and being the center of attention. When she beat No. 12 seed Dominika Cibulkova on Tuesday to become the youngest player to win a U.S. Open match since 1996, Bellis had every eye on her as she dropped to her knees in joy and surprise.

“I love it when people watch me,” Bellis said. “It gives me more energy and makes me play better.”

There will be many more eyes on the San Francisco native moving forward, starting Thursday with a second-round match against Zarina Diyas. How she handles it will be the test. Veteran players advise Bellis to focus on enjoying the moment, not the onslaught of attention.

“It’s not easy to manage this situation because she’s very young, but it will help a lot for her career,” said Simona Halep, the 22-year-old No. 2 seed. “It will be a good thing. I think she has more confidence now that she can be better than before this tournament.”

Bellis has never lacked self-assurance. USTA national coach Leo Azevedo, who occasionally works with Bellis , warned Bellis before her practice round on Wednesday that there might be a bigger crowd watching her. There wasn’t, but Bellis maintained her excellent posture, carrying herself like she was performing.

Her confidence and maturity for her age stood out to Azevedo when he began working with her more last year in conjunction with her full-time coach, her mother, Lori. A petite brunette with a freckled face, she looks 15 and enjoys the same things most 15-year-olds do — going to the mall, watching movies with friends — but her on-court poise is something Azevedo would expect from a more seasoned player.

“This is something you cannot teach,” Azevedo said. “Forehand you can teach. Backhand you can teach. With this technology today, everybody can hit the ball. The intangibles are very important.”

Bellis picked that up from her idol, Kim Clijsters. As Patrick McEnroe, the general manager for player development at the USTA, watched Bellis’s match Tuesday, he heard the fans around him echo Azevedo’s evaluation.

“She walks out like she expects to win,” McEnroe said. “She has a real presence about her on the court despite her small size. . . . I was sort of just listening in to random people talk, and they were like, ‘Wow, look at her, she looks like she belongs.’ It’ll be interesting to see how she handles the next match.”

She came to New York with credentials, earning a wild card berth into the main draw by virtue of winning the USTA girls’ 18s national championship, an impressive feat for a 15-year-old. The win over Cibulkova, however, was her WTA Tour debut.

Other young players have looked like they have belonged on this stage with surprising wins over high-ranked opponents, but then struggled later. Melanie Oudin beat Maria Sharapova in the 2009 U.S. Open and made the quarterfinals, but has since fallen in the rankings from No. 49 at the end of 2009 to No. 134.

Madison Keys was 16 when she advanced to the second round of the 2011 U.S. Open, and she has since fared better than Oudin. Keys, 19, is now one of the top American women, ranked No. 27.

“You can definitely get very nervous and you can really kind of start overthinking things and expecting a lot of yourself,” Keys said. “She just has to go out, have fun and keep playing. She has plenty of years ahead of her.”

Keys never had the desire to play college tennis, but Bellis is still unsure, so she said she will turn down the $60,420 she earned from winning her first-round match to stay an amateur. But she might take advantage of other perks that come with her surprising win.

“I love Ellen [DeGeneres],” Bellis said of a possible talk show appearance. “I think I would want to go on ‘Ellen.’ ”

Bellis played on a court that wasn’t shown on the regular television broadcast on Tuesday, but she’s scheduled to play on Court 17 in a late-afternoon match Thursday when she plays Diyas. Diyas said she expects there will be more pressure on Bellis now that she’s taken down Cibulkova, a former Grand Slam finalist.

There certainly will be more eyes on Bellis, waiting to see how she handles the second round.

“She likes this,” Azevedo said. “She likes it when people watch her. I think this is very important. The way she deals with the crowd and with the tournament, I don’t think it affects her at all.”