SANTA MARIA, Calif. – In what could be a deciding moment in the sex abuse case against Michael Jackson, the singer’s teenage accuser admitted yesterday that he twice told a school official that the King of Pop never molested him.

Even the prosecutor was taken by surprise by the boy’s bombshell on a day in which Jacko’s legal team hammered away at a series of damaging contradictions by the boy and his family.

The biggest blow came when the 15-year-old boy winced slightly and recounted a conversation he had with Dean Jeffery Alpert at his school in the spring of 2003.

“I told Dean Alpert he didn’t do anything to me. I told him two times,” he admitted after Jackson’s lawyer, Tom Mesereau, reminded him of the meeting.

Prosecutor Tom Sneddon – who apparently learned of the boy’s shocker over the weekend – tried to appear cool as the bombshell landed, but jurors’ pens were flying.

Under bruising cross-examination by Mesereau, the boy revealed prosecutors hustled him to an emergency meeting Sunday night to discuss the revelation.

“[Sneddon] asked me if I remembered who Mr. Alpert was,” the boy said.

The boy said he was sent to Alpert’s office at John Burroughs Middle School “because I was a discipline problem.”

The meeting took place after the boy had appeared nuzzling and holding hands with the singer in Martin Bashir’s documentary “Living with Michael Jackson.”

In a fatherly way, Alpert took the boy aside and asked whether Jackson had ever done “anything of a sexual nature” to him.

“I told him that Michael didn’t do anything to me,” the boy said.

“Mr. Alpert asked you twice?” Mesereau quizzed.

“Yes.”

“Didn’t Dean Alpert tell you ‘I can’t help you unless you tell me the truth … did anything bad happen?’ And your response was ‘No’?” Mesereau asked.

“Yeah,” the boy replied.

Jackson, dressed in an eye-popping red jacket, sat tall in his chair, chin up, index finger perched on his chin at times. After court, the pop star said, “Mesereau did a good job today.”

It was one of several contradictions that Mesereau highlighted during his grilling of the young accuser.

He had a field day with the boy’s school records, citing nine teachers who said he was a classroom nightmare and a list of offenses for fighting, disrupting class, refusing to obey teachers’ orders and being “defiant.”

“I wasn’t that good a kid then,” the boy admitted.

The kid’s school records contradict the testimony of his sister, who stubbornly denied he had disciplinary trouble at school.

In another coup for the defense, the boy admitted that many of the glowing things he and his family said about Jackson in a 90-minute rebuttal video were actually true.

His brother and sister had claimed the family was coerced into making the video on Feb.19, 2003.

When Mesereau focused on part of the tape where the boy’s mother praised Jackson saying, “He’s an honest man … a nice man,” the boy replied, “Yes, he’s a nice man. The things that he did was kind of dishonest. … Yes, Michael’s a nice man.”

But the boy didn’t give in when Mesereau asked, “Would you agree that you got very angry when you realized that Mr. Jackson was fading out of your life?”

“I never wanted to be in his family. I wasn’t looking for that,” the boy insisted.

The kid didn’t crack, but most legal analysts in the courtroom agreed Michael Jackson’s accuser lost his halo yesterday.

“It was a devastating day for the prosecution,” former Colorado sex-crimes prosecutor Craig Silverman said of the 15-year-old boy’s grilling by defense lawyer Tom Mesereau. “There were piles and piles of reasonable doubt today.”

CBS News chief legal analyst Andrew Cohen declared, “The prosecution was caught unaware. … This young man says ‘No, he didn’t molest me’ to a school official. … It’s bad for the prosecution.”

Loyola Law School professor Laurie Levenson, who saw the boy’s direct examination by District Attorney Tom Sneddon and his early cross-examination last week, noted indications that his key testimony was coached.

The boy was “inarticulate,” mumbled and was forgetful until the last 10 minutes of his testimony, when he described the alleged molestation, she said.

“Suddenly he was very polished, very certain, very articulate,” said Levenson.

She also said the boy showed no emotion when he detailed the alleged sex abuse but was clearly disturbed when he described how Jackson snubbed him once at Neverland.

“He was not angry at being molested. He was angry at being ditched,” Levenson said.

Legal analyst Trent Copeland said yesterday that the boy’s demeanor may also be a problem.

“This is the tale of two witnesses. On direct [being questioned by Sneddon], we saw a witness who was charming and cooperative,” Copeland said. “Now we’re seeing a witness who is uncooperative, petulant, evasive.”