SPRINGFIELD, Ill. — After finishing yesterday in second place at the LPGA's State Farm Classic, Michelle Wie was one good round away from finally living up to her deep potential.

Then, minutes after tapping in her bogey putt on the 18th green, Wie sat red-eyed at a folding table in front of a couple dozen baffled reporters and photographers, explaining why she'd been disqualified from the tournament.

The 18-year-old from Honolulu, playing her best golf of the year, broke one of the game's most basic rules: She failed to sign her scorecard before leaving the scoring area.

"I don't know why or how it happened," Wie said. "But it was an honest mistake."

Wie took no questions before leaving the clubhouse at Panther Creek Country Club. She climbed into an SUV with her parents and drove away.

That left Yani Tseng leading the tournament at 18 under, followed by Katie Futcher at 16 under and Hee-Won Han and Ji Young Oh another shot back.

Sue Witters, the LPGA's director of tournament competitions, disqualified Wie at the course after asking her what had happened.

"I felt like I was telling somebody that there was no Santa Claus," Witters said.

And with that, Wie was gone from a tournament where either the $255,000 winner's purse or the $155,252 second prize would have put her comfortably within the top 80 money winners for the year — and virtually guaranteed her a place on the LPGA Tour next year.

The State Farm seemed tailor-made for Wie, the Punahou School graduate who took time off from her freshman year at Stanford to try to become a full-fledged tour member for the first time.

Only two of the top 10 money winners were in town for the event, and Wie said before play began that she was looking forward to opening up her long game on the wide fairways at Panther Creek.

She shot a solid 67 on Thursday, then a 65 on Friday that tied her with Tseng, the woman who rallied to beat Wie in the final of the U.S. Women's Amateur Public Links in 2004.

Wie told reporters that after she finished her round Friday, she left the tent just above the ninth green where players sign their scorecards. She was chased down by volunteers working in the tent, who pointed out she hadn't signed.

Wie returned to the tent and signed the card. "I thought it would be OK," she said.

But Wie, according to Witters, had already walked outside the roped-off area around the tent. At that point, the mistake was final, Witters said.

Witters said she and other tour officials didn't learn about the mistake from volunteers until well after Wie teed off yesterday morning, so they let her finish the round.

"Is it real?" Tseng asked reporters just after Wie's qualification.

Without Wie, the tournament loses some of its luster, and likely some of the viewers who might have tuned into today's final round.

"She was one shot off the lead, she was going to help boost the ratings," said Christina Kim, who entered play yesterday as the leader before falling back to 12 under and a tie for seventh. "She was the player to beat this week."

LPGA veteran Betsy King, working as a TV analyst at the State Farm tournament, said that she always had her caddy stand over her as she turned in her scorecard, making sure nothing had been missed.

Wie said she usually signs her scorecard immediately, and had no idea why she didn't Friday.

"Hopefully it won't happen again," she said. "It was a good learning experience."

Tour officials and other players, while sympathetic, said the signature rule is at the heart of golf's honor system.

"Bottom line, we are held accountable to maintaining our scorecards and making sure that we attest the scorecard," Kim said. "But it's such a shame."