Barry Manilow is joining the likes of Elton John and Celine Dion, preparing for his huge opening night at the Las Vegas Hilton, and he gave "Extra's" Terri Seymour a backstage tour.

"I really didn't know it was going to be one of the most anticipated shows in Vegas," the modest Manilow admitted. "It's an honor to be on the same street as Elton and Celine and have my own room at the Hilton."

Barry's final dress rehearsal was in front of a packed house that included none other than Diane Sawyer, who actually joined Barry on stage for a surprise duet.

And Diane wasn't the only surprise for Mr. Manilow -- we introduced him to the Maynard triplets, the adorable "American Idol" sisters that "Extra" adopted, brought to Hollywood and began grooming for stardom after Simon Cowell called them "overweight Jessica Simpsons" on "Idol."

But Simon's comments are a distant memory for the sisters, who were thrilled to meet their idol. "I don't think we'd be singing today if not for you," the sisters told Barry. "You inspired us."

"And I'm so glad I've had a positive impact on your life," Manilow told them.

But Barry had more than just an impact on the Maynard sisters. In fact, two of the sisters were named after Manilow tunes. They also showed the legendary singer a snapshot of their mother singing with Manilow 20 years ago, and then they serenaded Barry with one of his own songs.

And that's when the unthinkable happened: a knocked-out Barry asked the girls, "Would you just come back and just do that for this crowd? You will blow them away."

That's right, the sisters were invited to be Barry's opening act for a night!

Needless to say, the girls were almost lost for words. "I'm still in shock," one admitted. "I tried as hard as I could not to cry, but we all cried," another said.

Stay tuned to "Extra" as we continue to follow the Maynard triplets' road to stardom. Next week… the return of Simon.