Some, including Nick Cannon, who witnessed 10-year-old Jackie Evancho sing live on Tuesday night’s episode of America’s Got Talent were in disbelief at the fourth grader’s mature voice. The Internet was also abuzz — with many speculating the 10-year-old soprano lip-synced her performance of “O Mio Babbino Caro.”

Judge Howie Mandel reiterated Wednesday that there is no lip-syncing allowed on the show and to prove a point asked Evancho to sing a few notes after she beat dancer Ryan Rodriguez to advance to the semifinals. She happily obliged and the audience responded with a roaring applause.

Evancho is no stranger to the spotlight, however. Her album, Prelude to a Dream, is available on iTunes and she’s performed with David Foster, who discovered Celine Dion and Michael Buble.

“Jackie’s a phenomenon,” Piers Morgan tells PEOPLE. “I’m more excited for her than I have been for any other performer, ever.”

Although most of the attention has been on Evancho, three other YouTube acts advanced to the semifinals on Wednesday’s show. Alexander Bui, a 16-year-old piano master, promised to deliver more modern music in the semifinals, despite judge Sharon Osbourne calling his performance boring. Magician Dan Sperry, who terrified Mandel after flinging used dental floss at the mysophobic judge, also made it through. And finally, the last spot went to singer Kristina Young.

“The bar is set so high for the singers now. I’m not sure either of them would’ve made much difference,” Morgan tells PEOPLE after casting the deciding vote for Young over singer Cam Hodges.

Next week’s episode will be a wild card show, with these favorite-but-eliminated acts getting a second chance: Michael Grasso, Connor Doran, Swing Shift Side Show, Kruti Dance Academy, Michael Lipari and Ashleigh Dejon, the Hot Shot Tap Dancers, RNG, CJ Dippa, Harmonica Pierre, Anna and Patryk, Doogie Horner and Rudi Macaggi. –MoMo Zhou