NEW YORK — While 15-year-old American CiCi Bellis was in the process of stunning a Grand Slam finalist to become the youngest player to win a U.S. Open match since 1996, her father did his best to conceal his emotions courtside.

Like many a teen, CiCi has strict rules for Dad in public — even if his 1,208th-ranked daughter is pulling out a back-and-forth 6-1, 4-6, 6-4 victory Tuesday over 12th-seeded Dominika Cibulkova in the first round at Flushing Meadows.

“I’m told I cannot sigh and I cannot move or say anything (because) that distracts her, so I just have to sit there like a Sphinx and just smile and pray,” the elder Bellis, Gordon, explained with a deadpan delivery. “She hears me when I sigh. So I can’t sigh.”

Ah, yes, the joys of raising kids. And make no mistake, Bellis is a kid. She is home-schooled and about to start 10th grade. Her first memory of the U.S. Open is watching on TV while Maria Sharapova played. She likes to hang out at the mall with friends back home in California. Asked whether she’s a fan of pop star Justin Bieber, Bellis answered, “I used to like him when I was younger, a couple years ago.”

Her victory was part of a 9-4 showing by American women Tuesday, including 8-0 against unseeded opponents. In an all-American match at night, another teen, Taylor Townsend, lost quickly to two-time defending champion Serena Williams 6-3, 6-1.

“We have such an amazing future,” Williams said about U.S. women’s tennis. “We have so much to look forward to.”

Her win came after Roger Federer beat Marinko Matosevic 6-3, 6-4, 7-6 (4) with Michael Jordan sitting in Federer’s guest box in Arthur Ashe Stadium.

“Growing up, he was my big sporting idol,” Federer said. “Having him here is unbelievably special.”

Aside from the Williams sisters, American tennis fans have not had much reason to cheer for their own in the latter stages of major tournaments in recent years. That’s why the occasional run by a young U.S. player — think Melanie Oudin, wearing “Believe” on her sneakers in 2009 — stirs interest at Flushing Meadows.

“Believing was the No. 1 thing that I had to do today,” said Bellis, whose nickname CiCi is derived from the initials of her first and middle names, Catherine Cartan.

Bellis plans on playing in the U.S. Open junior tournament. She lost in the third round of that event last year; she lost in the first round of the Wimbledon juniors last month.

But on Tuesday, there she was in front of a supportive, overflowing crowd on Court 6 at Flushing Meadows, taking it to Cibulkova, the Australian Open runner-up.

“I went into the match thinking it was going to be such a great experience,” said Bellis, whose rapid-fire sentences tend to finish with a gurgle of laughter, “but I never thought I would come out on top winning.”

Neither did her parents. Her mother, Lori, wasn’t there because she gets too nervous watching.