Britney Spears [1] closed out her four-year Las Vegas residency with an explosive performance on Sunday night [2]. The singer took the stage as part of her final Piece of Me show to perform the hit "Work B*tch" via satellite for New Year's Rockin' Eve With Ryan Seacrest [3], which took place in Times Square in NYC. Clad in a sparkly black ensemble with a diamond-encrusted heart on her butt, Britney looked incredible [4] as she delighted fans with her dance moves and stage presence. How amazing does she look? Watch her performance of "Work B*tch" above now, then look back on these nostalgic photos of Britney [5].