According to CNBC.com, the prevailing line for how long it would take Aguilera to sing the song, from first note to last, was 1 minute, 54 seconds, reports the New York Post.
Bodog.com timed Aguilera, who flubbed the start of one verse and may have added a word at the end, in 1:53.7.
However, because of the mistakes, a Sportsbook.com spokesman said that it was paying off both sides of a bet for the first time in its history.
The singer apologized later, saying she got caught up in the moment and lost her place.
"It was a controversial performance with bettors. Aguilera came in narrowly under, but it's hard to tell what impact her error had," said SportsInteraction.com betting analyst Al Dannity told the website.
"Had she remembered the lyrics, then she would probably have been more composed and finished faster. Those betting the over (might not) see it that way and I doubt they will be buying any of her records for some time," he added. (ANI)