updated 4:52 p.m. ET Jan. 26, 2008

ST. PAUL, Minn. - Mirai Nagasu’s mouth dropped open when she saw her scores. And that was before she realized she’d knocked off former world champion Kimmie Meissner.

“Wait, it’s 12 points?” Nagasu said, her eyes widening when she heard how big a lead she had on Meissner. “Wow. That’s exciting.”

Get used to it, kid. If the 14-year-old keeps skating like this, there’s going to be lots more excitement to come.

Nagasu pulled off one of the biggest upsets ever at the U.S. Figure Skating Championships on Thursday night. In her very first senior nationals — heck, her very first competition as a senior — the teenager won the short program with a spectacular performance that showed amazing flexibility, strong jumps and a presence on the ice well beyond her years.

Her score of 70.23 is the second-highest ever by an American woman in a short program, and it would stack up against anyone in the world. She had a 12.65 lead over Meissner, and it will be almost impossible for the defending national champion to beat her in Saturday’s free skate.

About the only one with a real shot at catching Nagasu is Ashley Wagner, second with 65.15 points. Rachael Flatt was third with 62.91 points. Even if Nagasu wins, though, she can’t go to the world championships because she’s too young.

“It was just fun out there,” Nagasu said. “I’m not going to let any of the pressure from being in first bother me.”

Reigning junior world champ Caroline Zhang said she wasn’t bothered by the expectations of her, but she sure didn’t live up to the hype with an uncharacteristically conservative program that has her in seventh place. She stepped out of the second jump on her triple flip-triple toe combination, and was so slow going into her double axel she almost came to a complete stop.

“I just wasn’t skating well for me,” Zhang said. “It just was a pretty slow performance.”

Nagasu’s precociousness is nothing new. She came to the national championships last year as a complete unknown — she’d never even made it to the final qualifier — and skated off with the junior title. She then finished second to Zhang at junior worlds, part of a 1-2-3 American sweep with Ashley Wagner.

But while Zhang and Wagner moved up to the senior ranks this fall — and right into the world spotlight — Nagasu stayed at the junior level to get more experience internationally. She routed the competition, winning everything she entered.

There’s a big difference between juniors and seniors, though, and no one quite knew what to expect from her here. She was so excited Wednesday night she couldn’t sleep, getting her in trouble with her mother.

“I think Mirai had a lot of nerves,” said her coach, Charlene Wong. “I just think she’s learning how to make it work for her.”

She had everything working Thursday night.

Skating to “I Got Rhythm,” she was a delight, a reminder of how beautiful and fun skating can be. She danced across the ice with playful footwork, and her bright smile made the entire audience feel as if it was dancing right along with her.

Her triple lutz-triple toe loop jump combination had exquisite flow, and her triple flip was effortless. But her most impressive elements were her spins and spirals, with a flexibility that would make Gumby look stiff. Other skaters may contort themselves into the same positions, but she does it with such grace it looks pretty, not painful. And she’s got some serious speed going, buzzing across the ice.

“My goal right now is to skate my best and have fun,” she said.

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