Nicole Castrale steals limelight with 64 - McDonald's LPGA Championship 2006

"I don't pay a whole lot of attention to leaderboards," Castrale said. "I saw it a couple of times. But really I was just trying to take care of myself and just hit fairways and greens out there today."

Sorenstam is seeking her fourth straight victory in the tournament. With her triumph last year, the Swedish superstar became the first LPGA player to win the same major three years in a row.

Last season, Wie finished second here to Sorenstam by three shots. In her two LPGA events this season, the 16-year-old from Hawaii has finished third and missed a playoff by a stroke each time.

Wie also made headlines Monday after she failed in her bid to qualify for the U.S. Open on the PGA Tour.

While Sorenstam and Wie always will be talked about, Castrale was the one who made the biggest headlines Thursday as she carded a bogey-free and career-low 8-under-par 64.

It was the round of a lifetime for Castrale, whose best career finish since joining the tour in 2002 was a tie for fourth at the Fields Open in February. The California native has undergone three rotator cuff surgeries and even lost her tour card in 2004.

"I wouldn't say I struggled," said Castrale, who won twice on the Futures Tour last year. "I would say I never put it all together. And there were parts of my game that were weaker than they were, and I needed to work on it. I needed to get better if I wanted to compete out here. It's a whole different ballgame out here."

Castrale has a two-shot lead over both Pat Hurst and Cristie Kerr. It is another stroke back to Christina Kim, Korean Seon Hwa Lee and Dorothy Delasin.

Castrale recorded three birdies on the front nine, another at No. 11 and then finished with four in five holes. She birdied Nos. 14-16.

With her huge day, Castrale made sure both Sorenstam and Wie would have a lot of work to do over the next three days.

Sorenstam and Wie both are seven shots back and tied for 41st after each carded a 1-under-71. Both were unspectacular the entire day.

Sorenstam played the front side at even after opening with a bogey. She also registered birdies at Nos. 10, 14 and 17 while sprinkling in bogeys at Nos. 12 and 15.

"I think it kind of summarized my year a little bit, so I'm not surprised," Sorenstam said.

Despite her round, Sorenstam was not disappointed.

"You can really hurt yourself on the first day," Sorenstam said. "I didn't do that all."

Wie struggled early, then got hot late. She overcame a double bogey at the par-4 sixth hole by birdying three of her final four holes. In between, she birdied No. 9 and bogeyed No. 12.

"I can't really explain it. But it felt like I played really well today," Wie said. "I couldn't really get anything going, but the last four holes seemed like I was back to normal. So hopefully tomorrow morning I can keep that going."