U.S. teenager Mirai Nagasu could be headed to a world figure skating championship sooner than even her biggest supporters expected, holding the lead after the woman's short program Friday.

Nagasu, 16, was at her charming and dynamic best at the Palavela in Turin, Italy, earning a career-high 70.40 points.

The Arcadia, Calif., native, who was fourth at the Vancouver Olympics, came out with a forceful triple-Lutz/triple-toe combination and then nailed her triple flip. But it was in the transitions where she outshone the competition, with intricate footwork and the best Bielman spin of the night.

Nagasu has dedicated this season to her mother, who is battling thyroid cancer. She could become the first woman from the U.S. to win the world championship since Kimmie Meisner in 2006 in Calgary.

Nagasu's position atop the leaderboard came as a result of Olympic champion Kim Yu-Na's surprising seventh-place place showing.

Kim, who has spent much of her time in recent years in Toronto working under the tutelage of former Canadian champion Brian Orser, started strongly with a triple-Lutz/triple-toe combination, but then had a bit of a lean on her triple flip heading into a doomed layback spin.

The 19-year-old paid the price for two attempts at the spin. The first, aborted attempt was the one evaluated by the judges, costing her valuable points.

"I felt very good at the warmup," said Kim. My first jump, the triple-triple, was really great. And then after that I felt I was ready to do a triple flip. It was really weird. I don't know what happened. It's the first time I missed the elements like that."

Kim later lost an edge on a spiral sequence.

The South Korean icon has admitted to difficulty in getting motivated for the event so soon after the Vancouver Games, where she was just about flawless.

She trails the leader by only 10.10 points but could be headed to her first defeat in 16 months. That defeat came at the Grand Prix final in late 2008 to Mao Asada of Japan.

Asada was in second place Friday with 68.08 points.

Olympic silver medallist Asada set the tone with tremendous height on her opening triple-Axel/double-toe, and seemed to float on the surface after her triple flip, but it was later revealed that she took off from the inside edge. Her Bielman spin later in the program was only slightly less impressive than Nagasu's.

"I think they will be back on their game tomorrow," said Nagasu of Kim and Asada. "I am sure they are tired after the Olympics, as I am, but I just have to concentrate on myself and do the best long program I can."

Finland's Laura Lepisto was on her way to putting together what was likely a career-best program when she stumbled on her last jump, a double Axel.

Olympic champ Kim Yu-Na of South Korea shrugs at coach Brian Orser after her short program setback. (Paul Chiasson/Canadian Press)

Lepisto, the 2009 European champion, got enough done before the bobble to sit third with 64.30 points.

Phaneuf on course for goal

Joannie Rochette of Île-Dupas, Que., is not competing at the world championships after her bronze-medal performance in Vancouver, which came just days after the death of her mother.

Cynthia Phaneuf, 22, of Contrecoeur, Que., is on course to set a personal best at the world championships. She returned to the world championship stage in 2009 after a four-year absence due to injuries and inconsistency.

Skating to Debussy's Nocturne, she earned 59.50 points for eighth place. Her only glaring mistake was a hand that touched down on a triple Lutz early in her routine.

"It's weird," Phaneuf said of Rochette's absence. "I always feel like she's coming soon, or she's going to arrive, because I've been competing with her in these competitions for so long, and she has always been there with me.

"I'm not going to not reach for a medal because she's not there. My goal was to be top 10, and it's still the same, and I'm going to go one step at a time even if Joannie's not there."

It was tough going for 22-year-old Myriane Samson in her first appearance at the world championships.

The Saint-Jean-sur-Richelieu, Que., native fell hard on her opening triple Lutz and later on a triple flip. Skating to Warsaw Concerto by Richard Addinsell, Samson displayed her artistic presence with strong step and spin sequences.

She scored 44.20 points but did not qualify for the top-24 free skate, finishing 29th.

Three-time European champion Carolina Kostner of Italy played it safe in her program, probably a good thing considering she fell out of the top 10 at both the Olympics and last year's world championships with a series of falls.

She had a clean opening triple-flip/double-toe combination and doubled out of a planned triple later in the program. Most important, the 2008 world silver medallist did not succumb to nerves or fall, landing in fourth place with 62.20 points to the delight of the home crowd.

The same can't be said for 2007 world champion Miki Ando of Japan, who fell on her first jump, a triple Lutz, en route to 11th.

Other medal contenders heading into Saturday's free skate include 17-year-olds Ksenia Makarova of Russia (fifth) and U.S. national champion Rachael Flatt (sixth).

With files from The Associated Press & The Canadian Press