While Khloe Kardashian's marriage is crumbling, her sister is having the time of her life.

Kourtney Kardashian went to Las Vegas for Labor Day weekend -- and partied her butt off at Hyde at The Bellagio on Saturday night.

The reality TV star was seen having a ball at the bash, which she attended wearing a very low-cut black top.

With her hair done up and sporting a sultry cat eye, Kourtney looked a lot like her other sister, Kim Kardashian.

Looks like we can officially kill those pregnancy rumors too -- as it looks like she was seen sipping champagne!

Check out more party pics above, plus see what she was wearing when she attended an event at Kardashian Khaos earlier in the day.

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