The singer sold over 130,000 copies of her winner's single Skyscraper over the past week to take the top spot, ChartsUpdate.co.uk reports this evening.
The original version of the song - as sung by US X Factor judge Demi Lovato - is at Number 37.
Sam easily made it to Number One, with her nearest competition selling less than half her total.
However Sam's sales are well down on James Arthur's huge 490,000 total for his first week on sale from last year.
In fact, Sam's track is the lowest selling winner's single for at least 5 years, going back to Leon Jackson's year in 2007.
X Factor judge Louis Walsh this week cast doubt on Sam's potential to become as big as some of the show's past winners.
"Sam will be No1 for Christmas. Then maybe one or two albums," he predicted, "I don’t know if she’s going to be a global superstar like Leona Lewis.
“She’s not a Beyoncé, at the same time she is a great singer and there is a market for her.”
But Louis declared: “She won’t be going back to cruise ships for a long long time.”