They're no strangers to swanky Sin City shindigs, and this past Saturday (May 2) Khloe and Kourtney Kardashian were spotted living it up in Las Vegas.

The "Keeping Up with the Kardashians" starlets headed over to the Sapphire Pool grand opening party at the Rio Hotel and Casino.

And both ladies looked absolutely beautiful as they posed for the paparazzi, with Khloe sporting a black tube dress with pink accents while Kourtney opted for a black strapless number.

Meanwhile their sister Kim and mother Kris Jenner were in Louisville, Kentucky at Churchill Downs for the Kentucky Derby, where they witnessed the second biggest upset in Derby history when Mine That Bird came from behind to win.

Enjoy the pictures of Kourtney and Khloe Kardashian partying at Sapphire (May 2).