Dec 14, 2009 4:00 AM EST
The Sing-off8/7c NBC Eight a cappella groups from around the country assemble to kick off NBC's four-night singing competition. The groups don't use b… Read more
Jennifer Hudson performs "The Christmas Song," "O Holy Night" and "Silent Night," and duets with Michael Bublé on "Baby It's Cold Outside" and "Let It Snow."
Premiered: December 14, 2009