Wie has been struggling with form and fitness in recent months
Michelle Wie was disqualified when lying second after three rounds of the State Farm Classic on Saturday.
The 18-year-old American had been enjoying her best tournament of the year, completing a third-round 67 to move to 17 under par.
But she had failed to immediately sign her scorecard on Friday, and it came to the attention of LPGA officials the following day.
"I don't know why or how it happened," said a tearful Wie.
"It's just really unfortunate. Usually I sign it first but I forgot to sign the scorecard.
"Unfortunately, I left the tournament area and a couple of the scorers went after me. And I signed it, and I turned it in, and I thought it would be OK.
It was an honest mistake on her behalf
LPGA director of tournament competitions
"But it was an honest mistake. I just forgot to sign it."
Sue Witters, the LPGA's director of tournament competitions, disqualified Wie in a small office in an LPGA trailer at the Panther Creek Country Club course after asking her what had happened.
"She was like a little kid after you tell them there's no Santa Claus," said Witters.
Wie said that after Friday's round she left the tent where players sign their scorecards and was immediately chased by some tournament volunteers who pointed out she had not signed.
But according to Witters, Wie had already walked outside the roped-off area around the tent, making the error irreversible.
"It was an honest mistake on her behalf," said Witters.
"Once it was brought to her attention, and we asked her to tell us what she recalled from yesterday once she got in the scoring tent, she about verbatim told us what we were told by a few of the volunteers.
"Never at any point did she try to deceive us. She couldn't have been more honest."