Affleck began his speech by thanking fellow nominee Denzel Washington.
It was neck-and-neck, but Casey Affleck was named Best Actor in the end.
After winning the SAG Award earlier this month, Denzel Washington became a last-minute favorite, but the Academy awarded the Manchester by the Sea actor with his first Oscar win. Affleck began his speech by thanking his fellow nominee.
"This means so much to me. Dammit. One of the first people who taught me how to act was Denzel Washington and I just met him tonight," he said, as the camera cut to an inscrutable Washington. "Thank you."
"Man, I wish I had something bigger and more meaningful to say, but I'm just glad to be a part of this community. I'm dumbfounded to be included," he told the crowd, taking the time to thank his costars, director and producers. "Thank you also to Matt Damon for creating this opportunity."
He concluded with a shout-out to his brother, saying, "Ben, I love you. You ain't heavy."
Manchester by the Sea took home an award earlier in the night, when Kenneth Lonergan won the Oscar for Best Original Screenplay. On the red carpet ahead of the show, Affleck told ET how watching brother Ben's career affected his own.
"It maybe seems hard from the outside but he's had a pretty good time and I've had a weird life," Affleck said. "I've been out here since I was 17 years old, and so I've gotten to know lots of actors who have had a lot of success and some failures and some hard times and some success again. I've been able to see other people's careers and how they've worked out and it's been an education."
