Britney's ready to bust it out this Sunday at the Billboard Music Awards in Las Vegas with a rumored TWO performances scheduled!

As Us Weekly report claims Brit will duet with Rihanna to open the show, performing "S&M." Spears participated in a remix of the hit single at Ri's request a few months ago.

Britney will also take the stage with tour partner Nicki Minaj to perform "'Till The World Ends."

The Billboard Music Awards air Sunday at 8 pm on ABC.