"Crash," featuring a huge cast in crisscrossing story lines over a chaotic 36-hour period in Los Angeles, rode a late surge of praise that lifted it past "Brokeback Mountain," a film that had won most other key Hollywood honors.
"We are humbled by the other nominees in this category. You have made this year one of the most breathtaking and stunning maverick years in American cinema," said "Crash" producer Cathy Schulman.
Lead-acting prizes went to Philip Seymour Hoffman as author Truman Capote in "Capote" and Reese Witherspoon as country singer June Carter in "Walk the Line," while corporate thrillers earned supporting-performer Oscars for George Clooney in "Syriana" and Rachel Weisz in "The Constant Gardener."
More than half the actors nominated for the awards-fest had never been up for an Oscar before. All four acting winners were first-time nominees, and all were expected to win, People Magazine Senior Editor Jess Cagle reports on The Early Show.
"Brokeback Mountain" filmmaker Ang Lee won best director for the tale of two old sheepherding pals who carry on a love affair they conceal from their families.
Lee, whose martial-arts epic "Crouching Tiger, Hidden Dragon" won the foreign-language Oscar five years ago, became the first Asian filmmaker to win Hollywood's main filmmaking honor.
"I wish I knew how to quit you," Lee told the audience crowd, reiterating the film's most-quoted line.
Witherspoon won a close race over Felicity Huffman in a gender-bending performance as a transsexual in "Transamerica."
"Oh, my goodness. I never thought I'd be here in my whole life growing up in Tennessee," said Witherspoon, who, like co-star Joaquin Phoenix as Carter's soul mate, country legend Johnny Cash, handled her own singing in "Walk the Line."
"People used to ask June how she was doing, and she would say I'm just trying to matter. I know what she means," said Witherspoon, who told the audience the Oscar made her feel she was doing work that matters.
Ryan Phillipe, Witherspoon's husband remarked to Smith, "What an amazing night, to see my wife up there, that last 30 minutes was just mind-blowing, man. To see her holding the Oscar after being together 10 years, and then for ("Crash") to win, it just blew me away."
Hoffman's performance nimbly straddles the magnetic qualities of raconteur Capote and the effete, off-putting egoism of the gay author.
"Wow, I'm in a category with some great, great, great actors, fantastic actors, and I'm overwhelmed. Really overwhelmed," said Hoffman, who asked the Oscar audience to congratulate his mother for bringing up four children alone.
"We're at the party, mom," Hoffman said. "Be proud mom, because I'm proud of you."
Clooney's win capped a remarkable year, during which he made Oscar history by becoming the first person nominated for acting in one movie and directing another.
Along with performing in "Syriana," Clooney directed the Edward R. Murrow tale "Good Night, and Good Luck," which earned him directing and writing nominations and was among the best-picture contenders.
In "Syriana," Clooney effaced his glamour-boy looks behind the bearded, heavyset facade of a CIA patriot who grows jaded over U.S. oil policy in the Middle East.
"All right, so I'm not winning director," the first-time winner joked, adding that an Oscar always would be synonymous with his name from then on, including in his obituary. "Oscar winner George Clooney, sexiest man alive 1997, 'Batman,' died today in a freak accident."
Clooney also lauded Oscar voters for their daring.
"This group of people gave Hattie McDaniel an Oscar in 1939 when blacks were still sitting in the back of theaters," Clooney said, referring to the supporting-actress winner from "Gone With the Wind," the first black performer to receive an Oscar.