Britney Spears closed out her four-year Las Vegas residency with an explosive performance on Sunday night. 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, 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 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.