Dean went first. They started playing music for a Dean Martin song that he happened to have been singing like an hour before, so he did pretty well. Knew all the words, even cranked out all the notes.
When they started playing Sam's song, I started laughing and yelled at getting_weary, who was in another room, "They're making Sam sing The Heart Will Go On from Titanic!" She ran out to watch.
When they'd started the music, Sam had laughed too, but I figured he at least knew which song it was. That belief was put away when he started singing Jingle Bell Rock. To Titanic music. Didn't work so well.
Needless to say, Dean won the contest.