Nizlopi's JCB song could deny Westlife their 14th UK number one on Sunday, latest sales figures suggest.
The JCB song is performed by a little-known duo from Warwickshire
Retailer HMV said the Irish boy band were marginally outsold by the relatively unknown duo on Monday.
However, it added that sales of Westlife's ballad When You Tell Me That You Love Me were expected to recover later in the week.
Meanwhile, bookmakers William Hill have made Nizlopi second favourites for this year's Christmas number one.
William Hill have made the winner of TV's X-Factor competition favourite to top the festive charts, with Westlife behind Nizlopi in third place.
The JCB song is performed by Luke Concannon and John Parker, a duo from Warwickshire.
It is a tale about a boy enjoying a ride in a JCB with his father and wishing he could use the empowerment he feels as he rides along to tackle bullies at his school.
Westlife's ballad enlists the help of Motown legend Diana Ross, who had a hit with this song back in 1991.
In a statement HMV said: "These Day One sales show that this week's chart will be a close run thing.
"Part of the problem for Westlife is that their Face to Face album continues to sell really well, with some fans preferring to access the track that way rather than buying it as a single."
HMV singles buyer Stewart Allan added that there had "definitely been a buzz building around Nizlopi".
"While it wouldn't be a complete shock if they pipped Westlife to the number one spot this week, I'd have to admit that it would still come as a bit of a surprise, especially after [Westlife's] stunning Record of the Year success at the weekend," he said.