NAGANO, Japan -- Irina Slutskaya moved into a commanding lead in the women's event at the World Figure Skating Championships on Friday after Michelle Kwan made a mistake in the short program.

Slutskaya was flawless in her routine, earning two perfect 6.0s for presentation to a Schubert melody. With a high triple lutz entering her combination, she also was the best of the afternoon for required elements, with all 5.8s or 5.9s.

"It's the first time I received 6.0 in the short program at the worlds," Slutskaya said. "I worked hard on my artistic marks and I'm very happy the judges see that, too."

Kwan dropped behind Fumie Suguri of Japan, who also skated without mistakes.

Kwan stumbled out of her triple lutz, in the first part of a combination. For that, she received technical marks between 5.2 and 5.4, very low for the four-time world champion.

"I didn't feel really good out there," Kwan said. "Heading into the triple lutz, the combination, I felt a little too fast and I think I leaned back a little bit."

She knows she has to do well Saturday.

"I have been in this situation before. You just have to skate, do your best and concentrate on your performance," she said.

Slutskaya has beaten Kwan all four times they met this season.

For Kwan to take her third consecutive world championship in Saturday's free skate, she needs to win the event and have someone else beat Slutskaya.

A jump from third is not out of the question, though. At the Olympics, Sarah Hughes leaped from fourth to upset both Slutskaya and Kwan to take the gold medal.

Hughes is not competing, saying she had too little training time following her victory in Salt Lake City a month ago.

Japan's Yoshie Onda was fourth, with American Sasha Cohen fifth. Cohen had an opportunity to do better until she stumbled on her final jump, a double axel.

The other American, Jennifer Kirk, Hughes' substitute here, was 15th. Bothered by a hip injury, she fell twice.

Russia's Maria Butyrskaya, who beat Slutskaya at this year's European championship, withdrew Friday morning before the short program, citing "physical and emotional fatigue," according to the official medical bulletin.

In the evening, Irina Lobacheva and Ilya Averbukh, with a tribute to the Sept. 11 terrorist attacks, captured the ice dance title.

It was the first world title for the Russians, who were fourth in the world in 2000. They were the silver medalists at the Olympics a month ago.

Second were Canadians Shae-Lynn Bourne and Victor Kraatz. Skating to a medley of Michael Jackson songs, they moved up from fourth a year ago.

Galit Chait and Sergei Sakhnovski won the first medal for Israel at the world championships with a bronze.

Lobacheva and Averbukh, who missed the first half of the season due to her knee injury, received firsts from seven of the nine judges to take the gold medal. It was the 25th gold medal for Russia or the former Soviet Union in the ice dance.

It was the second gold medal for the Russians in two days. On Thursday, Alexei Yagudin won his fourth world title, completing the three rounds of competition without a mistake. He scored two perfect 6.0s for presentation in the free skating, and he did two quads, including one as a part of a three-jump combination.

He became the first skater to win four major titles -- Grand Prix final, Europeans, Olympics and worlds -- in one season.