PIC: Rob Pattinson, Kristen Stewart Make Out at 'Elephants' Party

Pucker up!

Kristen Stewart knew exactly how to congratulate her man Robert Pattinson on his new movie Water for Elephants following its NYC premiere Sunday: With a big, sloppy kiss!

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Although Pattinson, 24, walked the red carpet without his lady love Stewart, 21, in NYC earlier that night, she accompanied her guy (and his parents!) for the swank afterparty, held at Le Cirque. See more photos of the two kissing.

"She looked amazing," an onlooker tells Us Weekly. As Pattinson received congrats from well-wishers, he and Stewart were inseparable at their table -- sipping beer rather than champagne -- throughout the elegant, formal affair. (Befitting the flick's circus theme, Le Cirque was decked out with brass birdcages, a brass elephant on a circus ball and other touches.)

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"They were a cute couple!" the witness says, adding that Stewart "got along together very well" with his mom and dad. As the group left around 1 a.m., Pattinson and Stewart were "hand in hand.. They were incredibly polite!"

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Another sweet couple in attendance: Reese Witherspoon and brand-new hubby Jim Toth. "People were coming up to her and wanted to cheers her wedding, she looked very happy," the witness says. Later in the night, the newlyweds snuck a kiss. Toth, 40, "was incredibly good at just standing back and supporting Reese," the observer says. The duo tied the knot in Ojai, Calif. in late March and honeymooned in Belize. The wedding "was a really nice day!" Witherspoon, 35, gushed on Good Morning America Monday.