Britney Spears put on a FREE show last night in Las Vegas and it sounds like it was an amazing 45 min performance!

In her first public performance since her successful Circus tour in 2009, Spears appeared on stage in front of a prop electric chair while singing "Hold It Against Me." With her boyfriend, Jason Trawick, and father, Jamie Spears, looking on from a VIP area, she later appeared inside an oversized boombox during the "Big Fat Bass" number, outfitted in a tight black outfit and policeman's cap.

Check out the rest of the story, including other costume changes, set list & how Jersey Shore's Pauly D was involved at