Holmes -- mom to Suri, 6, with ex-husband Tom Cruise, 50 -- was accompanied by her divorce attorney, Jonathan Wolfe, and his wife, Renee. "Jonathan rarely left Katie's side," an attendee tells Us Weekly. "With a champagne flute in hand, Katie posed for several fan photos as guests pointed their iPhone cameras in her direction."
The actress also spent the evening chatting with her Dead Accounts director Jack O'Brien. "Katie enjoyed two or three glasses of champagne and, by the latter half of the evening, was double-fisting the champagne in one hand with a Diet Coke in the other," the attendee says of the Dawson's Creek alum, who "appeared to genuinely have a good time throughout the night."
When the caroling began, the Ohio native "was heavily engrossed in the performances," according to the attendee. Holmes and her attorney left the gala just before 9:30 p.m.
Holmes -- who currently resides in a $12,500-a-month apartment in Manhattan's Chelsea neighborhood -- has earned positive reviews for her performance in Dead Accounts, in which she plays a woman whose con-man brother (Norbert Leo Butz) unexpectedly returns home from New York; the play itself, however, has received mixed reactions.
Holmes -- who made her Broadway debut in the 2008 revival of All My Sons (opposite Patrick Wilson) -- thrives in live theater. "It's exciting because there's no close-up, so a person has to use every inch of themselves," she recently told Vogue. "So you're never done -- and who wants to be done? It's just another opportunity to keep growing."