'Mercy' debuts at number one on the strength of download sales alone, seeing off a challenge from Nickelback slow-burner 'Rockstar', which settles for two.
Also entering the top ten this week is dance track 'What's It Gonna Be', from H 'two' O and Platnum at seven, while The Feeling rise to nine with 'I Thought It Was Over'. Goldfrapp round off the top ten with 'A&E'.
Elsewhere, OneRepublic chart at twelve with 'Stop and Stare', three weeks ahead of its physical release, and Paramore climb 40 places to 17 with 'Misery Business'.
The UK top ten singles in full:
1. (-) Duffy: 'Mercy'
2. (2) Nickelback: 'Rockstar'
3. (1) Basshunter: 'Now You're Gone'
4. (5) David Jordan: 'Sun Goes Down'
5. (3) Adele: 'Chasing Pavements'
6. (4) Rihanna: 'Don't Stop The Music'
7. (-) H 'two' O ft. Platnum: 'What's It Gonna Be'
8. (6) Kelly Rowland: 'Work'
9. (12) The Feeling: 'I Thought It Was Over'
10. (18) Goldfrapp: 'A&E'
> Has Jack Johnson made it two weeks atop the albums chart? Click here to find out!