The controversial cowboy love story also earned the best director trophy for Ang Lee and a supporting actress win for Michelle Williams, who shared honors with "Junebug" star Amy Adams in the ceremony at the Santa Monica Civic Auditorium.
The Critics' Choice Awards, the first major televised gala of the awards season, are chosen by the Broadcast Film Critics Assn. Five of the past six winners of the Critics' Choice award for best picture have gone on to claim the top Academy Award.
"I used to say that I didn't believe in competition among filmmakers, but — what the hell — this is great!" Lee roared in his acceptance speech.
"Brokeback" producer and co-writer Diana Ossana appeared overwhelmed by the film's success as she accepted the best picture prize. Addressing her collaborator, Ossana asked, "Ang, weren't we making a film that nobody was supposed to see?"
Not only are people seeing the controversial love story about gay cowboys, they're also rewarding it. "Brokeback Mountain" has already been voted best of 2005 by film critics' groups in Los Angeles, New York, Boston, Dallas and San Francisco.
But because the BFCA is the nation's largest group of film reviewers — its 200 members range from "Good Morning America's" Joel Siegel to critics at dozens of local TV stations — its selections resonate with Academy voters.
"Brokeback" star Heath Ledger lost the best actor award to "Capote" star Philip Seymour Hoffman, who surprised the audience with his candor at the podium while thanking his film colleagues for their patience during production. "I'm not the easiest guy to work with," he confessed.
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"I love critics!" shouted an ecstatic Reese Witherspoon as she gleefully accepted the best actress award for portraying June Carter in "Walk the Line." "This year anyway," she added slyly. "I was incredibly intimidated by this role and I didn't think I could do it."
Equally ebullient was supporting actress co-champion Adams, who saw her win as a victory for all small films. "Can you believe we made this for less than a million dollars?" she said. "Any of you out there who has a small movie to make, I'm telling you: Do it!"
Paul Giamatti pulled off the biggest upset of the night, calling his win for best supporting actor a "big surprise." Giamatti was hailed for portraying a never-say-die boxing coach in "Cinderella Man."
Most pundits expected the winner to be George Clooney for "Syriana." Clooney also came away empty in bids for best director and screenplay for "Good Night, and Good Luck."
But Clooney didn't walk away empty handed. The BFCA presented him with its honorary Freedom Award for shining "his light on a crucial moment in our history illustrating the impact and importance of courage and integrity in broadcast journalism."
"Crash" won screenplay award as well as the prize for best acting ensemble. Writer-director Paul Haggis accepted the scripter trophy, admitting, "We never thought we'd get this movie made."