'Under Pressure (Ice Ice Baby)', the Irish twins' collaboration with Vanilla Ice, is just 24 copies behind 'Fireflies', having shifted over 24,000 copies in two days.
The song was made available to download from Sunday and will be physically released on February 15.
Owl City - a.k.a. US synth-pop singer-songwriter Adam Young - has spent the past two weeks at number one in the UK. He also leads the Australian and Irish singles charts, having reached the summit of the Billboard Hot 100 last October.
Meanwhile, the Glee Cast are currently in third position with 'Don't Stop Believin', while Iyaz's 'Replay' is at four. 3OH!3 complete the top five with their Katy Perry collaboration 'Starstrukk'.
> Click here for this week's top ten singles