Usher has ended Scouting For Girls' two-week reign over the UK singles chart.
'OMG' - featuring, co-written and produced by Black Eyed Peas star will.i.am - climbs from number two to the top spot, forcing Scouting's 'This Ain't A Love Song' into second place.
It is the fourth UK No.1 for Usher, who previously reached the top with 'You Make Me Wanna' (1998), 'Yeah!' (2004) and 'Burn' (2004).
The highest new entry of the week comes from London rapper Professor Green, who makes his chart debut at number three with 'I Need You Tonight', a track built around a sample from INXS's 1987 hit 'Need You Tonight'.
Meanwhile, Kelis notches up her ninth top ten hit - and first chart entry in more than three years - after debuting at five with 'Acapella'.
Disney star Selena Gomez also enters the top ten this week, landing at seven with her UK debut 'Naturally'.
Outside of the top ten, Taio Cruz leaps from 40 to 12 with Ke$ha collaboration 'Dirty Picture', while Kate Nash debuts at 15 with 'Do Wah Doo'.
The top ten singles in full (click where possible for videos):
1. (2) Usher ft. will.i.am: 'OMG'
2. (1) Scouting For Girls: 'This Ain't A Love Song'
3. (-) Professor Green ft. Ed Drewett: 'I Need You Tonight'
4. (3) Plan B: 'She Said'
5. (-) Kelis: 'Acapella'
6. (4) Lady GaGa ft. Beyoncé: 'Telephone'
7. (-) Selena Gomez & The Scene: 'Naturally'
8. (6) Timbaland ft. Justin Timberlake: 'Carry Out'
9. (5) Tinie Tempah: 'Pass Out'
10. (7) INNA: 'Hot'
Source: Official Charts Company
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