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Christina Aguilera was apparently feeling a little too festive at Seth MacFarlane's annual Christmas bash, so much so that a guest said she was "wasted" and needed boyfriend Matt Rutler's assistance leaving because she couldn't exactly walk straight.

The New York Post said Christina was one of many famous faces on hand at the "Family Guy" creator's bash, including Meghan Trainor, Katharine McPhee, Bill Maher, Zac Efron, Marilyn Manson and others. As usual, the party was over-the-top with a 50-piece orchestra and Seth singing Frank Sinatra tunes as Tina Sinatra looked on.

As the evening progressed, Seth asked many of his guests to join him for a song. Most did, but Christina didn't, despite the two of them having sung "New York, New York" at the Lincoln Center concert "Sinatra: Voice for a Century" on Dec. 3.

"Seth asked her five times to come up [and sing] and she refused," a source said, adding that she seemed hesitant because she'd been drinking somewhat liberally. "She was a mess. The reason she didn't get up is because she was wasted."

At one point, "she nearly fell into a Christmas tree," the source added.

It seems that she was feeling a bit woozy when she left the party, too.

"[Matt] and her girlfriend had to hold her on each arm walking out," the source said. "She was wearing 6-inch custom Louboutins. She was literally wobbling."

As for everyone else, the party seemed to be a rousing success.

Guests entered the party through a "giant snow globe that doubled as a photo booth," the source said, adding that there was also a bar that had vintage crystal from the 1940s and an "ugly sweater workshop."