He said it was the singing that was his biggest challenge.
"Ultimately the song was like six minutes, and the chorus stretched on and on because they kept getting more and more celebrities," Affleck told Entertainment Weekly. "I think one verse was taken out. Which is a good thing: I am not a strong singer. When we're going nose to nose, you'll see - or you'll hear - that I'm not singing in the range I'm supposed to. And I'm not keeping time. I don't think this is going to prove a successful reel for any musicals."
Apparently, Damon's best pal Affleck was a big fan of Silverman's video and was more than happy to participate in the response when Kimmel's producers came calling.
"I have a lot of respect for the group over there - they're really good comedians - so I just committed to it," he said. "Everything I got from them was really funny and made me excited."
The video, which is available on the ABC Web site, also featured cameos by Hollywood A-listers including Brad Pitt, Cameron Diaz, Robin Williams, Don Cheadle and Harrison Ford. Affleck said he's a huge fan of Ford's and was thrilled when the rugged actor immediately said yes to the role. Ford had no problems with his scene: pulling up to a light in a convertible next to Affleck and Kimmel's car, and then blowing kisses at the "couple."
"It's the most incongruous moment in the thing because he's the most rugged, masculine guy in the world, and there he is in his West Hollywood outfit blowing kisses," Affleck said.
By Judy Rosen