Tribeca 2012: Jason Segel, Michelle Williams Draw Buzz at 'Five-Year Engagement' Party

The undeniably cute, seemingly improbable romance between Jason Segel and Michelle Williams became official at the Tribeca Film Festival's opening night party celebrating Segel's latest film, The Five-Year Engagement.

our editor recommends

'Jeff, Who Lives at Home' Star Jason Segel on His Secret Athleticism and Improvising With Ed Helms (Video)

Tribeca 2012: Emily Blunt Gives Her Cookie Monster Impression, Talks 'Five-Year Engagement' and 'Looper' (Video)

In recent weeks, the lanky goofball and the Oscar-nominated pixie have been romantically linked in the tabloids and spotted hanging out with Williams' daughter, Matilda, in the actress' Brooklyn neighborhood.

Enter a new A-list pairing, more approachable than Brangelina, perhaps: On Wednesday night, Williams -- private, demure, usually seen at these sorts of things with best friend Busy Phillips by her side -- joined Segel for the premiere of Engagement and the after-party at The Museum of Modern Art in New York City. The couple sat together at the screening in the Ziegfield Theater, then hopped over to MoMa, where they held court with Segel's co-star Emily Blunt, festival founder Robert De Niro and Hunger Games star Elizabeth Banks, among other boldfaced names.

PHOTOS: 10 of Tribeca 2012's Films to Watch

Segel, suited-up like Barney Stinson, grinned like he'd just won the lottery, laughing with Williams as they mingled with fellow partygoers. The press-shy Williams, who wouldn't be interviewed, wore a black, '50s-style party dress with a flared skirt, her Mia Farrow haircut perfectly coiffed to inspire copycat 'dos.

"I just think it's really sweet," actress Leelee Sobieski told THR of the Segel-Williams matchup, adding: "It makes me happy too. I think it makes everybody happy. When everybody blesses a union between two people for some reason, it's great! The whole world sending a positive energy for two people to be happy. That's nice."

Meanwhile, Segel was mum as Williams on the new love, saying his favorite moment of Tribeca was meeting De Niro. "It was the coolest thing of all time," gushed the actor, who co-wrote Engagement with director Nicolas Stoller.

VIDEO: Emily Blunt Gives Her Cookie Monster Impression

The Judd Apatow-produced film, which received a positive review by THR's John DeFore, features Segel and Blunt as an engaged couple whose relationship is put to the test amid life's hurdles. Blunt, letting loose at the party, said her favorite thing about the Tribeca Film Festival is "the New York crowds," observing: "They are trustworthy in their reaction so I'm glad they liked (the movie) tonight."

The museum was lit up with electric-pink lighting, towers of pink cupcakes and a wedding-themed buffet featuring arctic char, onion rings and macaroni and cheese.

"This is really bizarre," said Engagement actress Dakota Johnson, soaking in the spectacle. "It's the biggest party that I've ever been to for a film, and it's crazy that I'm in that film! ... And I also think it's really funny that all the waiters are wearing pink ties. I'm sure they hate it. Maybe some of them really like it?"

was the man of hour at Wednesday night's Tribeca

and Michelle Williams