When Miley Cyrus took the iHeartRadio Music Festival stage Saturday night for a performance of her rebellious hit single, "We Can't Stop," it was decidedly toned down from her much-talked-about VMA performance. And even though she didn't stick out her tongue or get down and dirty with a foam finger this time out, she did smack a dwarf's rear end as she twerked with abandon in high-cut jean shorts.

Sin City's newest resident performer, Britney Spears, was the one to introduce pop music's newest princess, telling the sold-out crowd at Las Vegas' MGM Grand Arena night, "My girl's about to get to work, bitch."

Dressed in a revealing, fur-sleeved white dress with breast pasties poking through, the Bangerz singer sang the Mike Will Made It-produced "do what we want" party anthem as people dressed in mushroom, rainbow and flower costumes danced whimsically about. The always-provocative chanteuse stalked the stage, singing into her banana microphone, while the smilers in the audience sang along on cue.

Slowing things down, Cyrus then took a seat for her cover of Melanie Safka's "What Have They Done To My Song Ma." The acoustic guitar ballad featured lyrics about the stresses of superstardom: "Look what they've done to my soul/ Yeah, they tied it in a plastic bag/ And they shook me upside down, Ma."

"I had my first #1 on Billboard with this song," Cyrus said, thanking the crowd for their support before diving into her first-ever live performance of "Wrecking Ball."

As images of collapsing buildings played on the video screen behind her, Cyrus was brought to tears onstage as she performed on bended knee. After saying goodnight to all the festival goers, Cyrus, whose MTV documentary "Miley: The Movement" premieres Wednesday, October 2, briefly toggled from sultry diva to wild child and rocked out to the guitar solo on her way off stage.