Upon taking the stage to accept his award, Day-Lewis knelt before presenter Helen Mirren, who won the best actress Oscar last year for her work in "The Queen," and she gamely tapped Day-Lewis on the shoulder with the statuette as if to knight him.
"That's the closest I'll ever come to getting a knighthood, so thank you," he said.
"My deepest thanks to the members of the (Academy of Motion Picture Arts and Sciences) for whacking me with the handsomest bludgeon in town."
The British actor said the film made him reflect on the relationships between fathers and sons, and so he accepted the prize in memory of his late father and grandfather, and on behalf of his own "three fine boys."
It was Day-Lewis' second Oscar. He previously won for his performance in the 1989 film "My Left Foot."
"There Will Be Blood" also earned the Oscar for cinematography.
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