Haters to the left! Britney Spears showed she's back in a big way -- and in fighting shape -- at her Piece of Me debut performance Friday night (Dec. 27) in Las Vegas.

Flanked by guests including Miley Cyrus, Katy Perry and Selena Gomez, Spears was obviously and appropriately the star of her own show. With a set list that included old favorites as well as new tracks like "Perfume," Spears aimed to please -- and she did.

Though the "Baby One More Time" singer was criticized in recent tours for not dancing much, Spears brought it big time for her comeback shows. Despite multiple knee surgeries that hindered her movement slightly before, Spears danced her uber-toned behind off, showing her lessers and her lovers how it's done.

She didn't just deliver a "Piece" of herself. The proud mom of two gave it her all, and it showed.

Watch Britney Spears Perform 'Me Against the Music'

Watch Britney Spears Perform 'Work Bitch'

Watch Britney Spears Perform 'Circus'

Watch Britney Spears Perform 'I Wanna Go'

Watch Britney Spears Perform 'Baby One More Time' + 'Oops ... I Did It Again'

Watch Britney Spears Perform 'Gimme More' + 'Break the Ice'

Watch Britney Spears Perform 'Toxic'

Watch Britney Spears Perform 'Boys' + 'Perfume'

Watch Britney Spears Perform 'Freakshow'

Watch Britney Spears Perform 'Do Somethin''

Watch Britney Spears Perform 'Drive Me Crazy'

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