Justin Timberlake, Jessica Biel Party With Pals in Sin City

Matt Donnelly
OMG Relationships
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Newlyweds Justin Timberlake and Jessica Biel jetted to Las Vegas together this weekend ... to party separately.

Both halves of the Hollywood pair came to celebrate mutual friends' respective bachelor and bachelorette parties: Justin and a pack of boys toasted the groom-to-be, while Jessica got down with the future bride.

Kicking off on Friday, Timberlake and company hit the Bellagio's Yellowtail for dinner, snacking on sushi and sashimi and of enjoying plenty of sake.

An omg! onlooker says the men cheered loudly in the eatery while Biel and the girls enjoyed American fare directly across the hall at the hotel's Fix restaurant.

Chicken wings, tuna tartar, and other small plates were passed, and the ladies made toasts to their guest of honor.

Perhaps Friday proved too much for the guys – they dropped off the radar the next day, while Biel and her party had their run of the strip.

One source tells us the pack of women luxuriated at the spa at Caesar's Palace Saturday afternoon before glamming up for dinner. This time it was the ladies' turn to sample the Japanese cuisine at Yellowtail. (Maybe their men recommended it?)

After the meal, the girls descended on the Mirage Hotel & Casino's night spot 1OAK, where they were greeted with a fully stocked table of vodka, champagne, and Fireball (cinnamon flavored whiskey, popular for group shots), which all helped the ladies party past 3 a.m., beside folks like Olympian Michael Phelps and his new lady Sarah Herndon.

We can't say we're surprised Biel dominated the Vegas weekend -- Timberlake is probably still walking off this little tequila stunt.

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