Holly Madison is no stranger to flashing her "enhanced" assets to the world, but it seems the former Playgirl got a little bit of unplanned rehearsal for her upcoming role in the topless production "Peepshow" while partying in Sin City on Saturday night.

According to an eyewitness, Madison was left a little red-faced at Niche Media’s Vegas magazine soiree at PURE nightclub when the top of her dress popped open in front of a group of high-brow guests.

PHOTOS: Click here to see photos of Holly Madison.

"She was embarrassed but was humbly laughing about the whole thing," said our inside source.

Madison will replace "Dancing With the Stars" champ Kelly Monaco's racy role in "Peepshow," which also stars former Spice Girl Mel B.

RELATED: Click here to learn more about "Peepshow," starring Mel. B.

RELATED: Click here to read about Mel. B and Kelly Monaco's poolside "Peepshow" party.