Among them, Miley Cyrus was right in the front row and she got some extra special attention from Britney's backup dancers.
At one point, the dancers jumped down and started grinding with Miley and she even simulated a kiss with one of them during the dirty dancing sesh.
While Miley sort of stole the show, Britney was still super grateful that she showed up.
"@MileyCyrus Love you so much! Thank you for coming to #PieceOfMe! I adore you :)" she tweeted after the show.
Katy Perry was also in the audience, but according to TMZ, she didn't get as much of a kick out of it as Miley did.
Check out the videos below to see Miley get down during Brit's big debut.