The singers performed McBride's "Marry Me."
Christina Davidson and Frank Tucci's ceremony -- quick even for a Vegas wedding -- went on behind the singers during the performance and fans could hear the bride and groom say "I will" before their first kiss as a married couple, bringing the crowd to its feet.
Meanwhile, Taylor Swift won her second consecutive entertainer of the year ACM award, just 24 hours after she was saluted by first lady Michelle Obama for her charity work on The Kids' Choice Awards. Swift became just the second woman to win the award twice since Carrie Underwood.
After hugging her way to the stage, Swift, 22, took a moment to say hello to Kevin McGuire and his family. McGuire, a high school football player who has cancer, was to have been her date to the awards but was hospitalized and couldn't make it. "He's not here but I promised him I would give him a shoutout," she said.
Swift beat out an all-male field that included Kenny Chesney, who was shut out at the awards after leading all nominees nine. Miranda Lambert, Jason Aldean and Kelly Clarkson were the night's top winners with two awards apiece.
The Eli Young Band's smash "Crazy Girl" brought the Texas quartet its first win, for song of the year. Thompson Square took vocal duo of the year over Sugarland in an early award. "American Idol" winner Scotty McCreery won the fan-voted new artist of the year. Toby Keith won video of the year for "Red Solo Cup."