The group hit the number one slot last night with their cover of Damien Rice's hit Cannonball.
But despite the huge exposure of the group with more than 15 million viewers tuning in to watch the X Factor reach its climax, the track sold 210,000 copies in its first week.
The Little Mix track sold less than half of 2010 winner Matt Cardle's first week tally of 439,000.
And its sales are dwarfed by the success of past winners such as 2005 champion Shayne Ward whose That's My Goal sold 742,180.
Single releases are usually timed to coincide with the week of the Christmas number one, but this year programme bosses released the track a week earlier.
Gareth Malone's choir of Military Wives is now favourite to take the prized festive top slot which will be announced on Christmas Day itself.
Little Mix even finished behind 2007's little-remembered winner Leon Jackson who shifted nearly 276,000 copies of his debut When You Believe in the first week.
The only past winner which the all-female quartet have outsold is Steve Brookstein who triumphed in 2004, when The X Factor was in its infancy.
Brookstein sold almost 128,000 copies of his single Against All Odds in a week.
However Little Mix can take some comfort from the fact their single achieved the biggest first week sales for a single so far this year. And it outsold the rest of this week's Official Singles Chart top five combined.