Bookmaker William Hill has suspended betting on the UK's Christmas number one after a flurry of bets made the betting "unviable".
Rage Against The Machine widened the gap over X Factor winner Joe McElderry in the battle for the top spot, building up a lead of more than 60,000 sales by Wednesday.
A William Hill spokesman said 98% of the bets were for the US rock band - and the firm had to keep adjusting the prices until it became the favourite.
Bets of up to £1,000 were being placed for the expletive-littered song and the company would lose a six-figure song if it tops Sunday's chart.
The Los Angeles band's track Killing In The Name - originally released in 1992 - and McElderry's song The Climb together account for nearly 300,000 sales so far this week.
The surprise contenders praised the internet campaign which has driven their sales and declared: "Let the people decide."
However, the situation could soon change with the release of a CD version of the 18-year-old X Factor star's single. Until Wednesday the track was only available on download but it is thought many people will buy the CD as a stocking filler.
The Christmas sales can buck the overall trend for CDs making up less than 2% of singles sales.
HMV spokesman Gennaro Castaldo said on Wednesday: "It's going to be a much closer race than anyone would have predicted a few weeks ago, but we remain confident that Joe will win out in the end to claim the Christmas number one and the fifth in a row for the X Factor.
"More than 1,000 fans braved the wintry conditions to queue outside Joe's home town HMV in South Shields from early this morning in the hope of meeting the X Factor star."
