Britney Spears and Rihanna took the stage at the MGM Grand Arena to open the Billboard Awards in Las Vegas tonight. The duo performed Rihanna's hit "S&M" and shared a sexy almost kiss in between belting out the lyrics. It was Britney's first appearance of the night, since she's also set to take the microphone with Nicki Minaj. Rihanna's up for 18 awards, including Top Artist, Top Female Artist, and Top R&B Artist while Nicki was nominated for four. Britney isn't up for any prizes at the event, though now that the show is returning after a five-year break, she should be able to snag a few in 2012 for her work on Femme Fatale.