Just hours after testifying Tuesday, Leno was skewering Jackson again as he taped Tuesday night's show in Burbank.
"OK, you know the worst part about testifying, I had to follow the chimp. The witness chair was a mess," Leno told his audience.
And Leno had quipped on Monday's show: "I was called by the defense. Apparently they've never seen this program."
But there he was on the stand Tuesday on a star-studded day in court, amusing jurors with the occasional aside and providing Jackson's defense with his own suspicions of the boy accusing the pop singer of molestation.
Defense attorneys called Leno to support their claim that the boy's family schemed to get money from celebrities like Jackson. The boy was suffering from cancer when he telephoned the talk show host.
Later in the day, the defense called actor Chris Tucker to the stand and said he would be their last witness, indicating Jackson will not testify. Defense attorney Thomas Mesereau Jr. fueled speculation the pop singer might take the stand in opening statements, when he said jurors would hear from Jackson on certain issues.
Tucker remained on the stand at the end of the day and was scheduled to finish testifying Wednesday morning, CBS News Correspondent Steve Futterman reports.
Tucker was very close to the accuser and his family around the time the alleged molestation took place.
According to Futterman, when Tucker wraps up, the prosecution plans to present a series of rebuttal witness, which should take two days. Closing arguments should come next week.
Initially serious and understated on the witness stand, Leno warmed up during his testimony, occasionally smiling, and finished with a lighthearted promo: "We have Renee Zellweger on the show tonight."
Leno made a few other wisecracks that drew laughter from jurors.
"I'm not Batman," he joked as he explained why he thought it odd that a boy would be calling a comedian in his mid-50s to tell him he was the youngster's hero.
But Leno's testimony neither boosted nor busted Jackson, CBS News Legal Analyst Andrew Cohen said.
"Leno was never going to be a make-or-break witness for the defense but certainly they seem to have oversold him to jurors," Cohen said "During opening statements, Jackson's attorneys told the panel that Leno would help show a pattern of manipulation on the part of the accuser and his mother and I'm not sure Leno delivered on that promise."
Leno said the boy left so many voice messages that he finally approached comedian Louise Palanker, a friend who had become acquainted with the boy.
"I said, 'What's the story here? This doesn't sound like a 12-year-old. This seems a little scripted,'" Leno testified. He said Palanker told him the boy wanted to be a comedian and writes out everything he says.
Leno testified he makes many calls to ill children, and at one point did an imitation of the mumbly way children usually speak to him — not the kind of forceful, adult presentation he said he heard from Jackson's accuser.
But Leno said the boy never asked for money and he never gave him any, though he did send "Tonight Show" memorabilia and a picture.
The defense has said Leno was so concerned about the boy's calls that he called police, but Leno said Tuesday it was police who contacted him. He said he probably did tell police he believed the family was looking for money.
"In the business I'm in you hear from a lot of crazy people and I'm reluctant to follow up. But when it's a child I do follow up," he testified.
Prior to Leno's testimony CBS News Consultant J. Randy Taraborrelli said on CBS News' The Early Show that this would be the first time that Jackson and Leno locked eyes since Leno has been making jokes about Michael Jackson practically every night for the last six months.
"I can tell you that Michael Jackson has not found those jokes humorous," said Taraborrelli, who has been in close contact with the Jackson camp. "Jackson feels that Jay has been very unkind, very mean, and that his life is on the line."
Later Tuesday, Tucker testified that he met Jackson's accuser after the boy's father introduced himself at a comedy club and asked him to take part in a benefit.
Tucker said that a few days after the benefit, the boy told him it hadn't made any money, so Tucker wired "probably $1,500 or more" to a foundation for the family.
Mesereau asked Tucker if he believed the money was for medical expenses.