Was Mariah Carey Actually Singing On The 'Christmas In Rockefeller Center' Special?

Below is a video of Mariah Carey "singing" her XXXmas jam "Oh Santa" on the Christmas In Rockefeller Center special that aired on NBC last night (watch Kylie Minogue, Susan Boyle, Jackie Evancho and Annie Lennox here).

At first I had my doubts that Mimi was actually doing this song live, but upon another viewing it seems she was maybe at least doing a bit of ad-libbing over a tape. Either way, she opened the show and it was still a fun, energetic spectacle.

What do you think? Was the Original Chart Rigger pulling a fast one by mouthing the words to her Merry Christmas II You tune?