Usher has returned to the top of the Billboard Hot 100, preventing Katy Perry from scoring a No.1 debut.

‘OMG’, which became the R&B star’s ninth US No.1 a fortnight ago before being knocked off by Eminem’s ‘Not Afraid’ seven days later, bounces back to pole position this week.

Perry has to settle for a number two debut with ‘California Gurls’, the Snoop Dogg-assisted trailer from her upcoming second album Teenage Dream.

Meanwhile, rapper B.o.B places two singles in this week’s top five: ‘Airplanes’ at three and former No.1 ‘Nothin’ On You’ at four.

Eminem’s ‘Not Afraid’ slides to six after just one week on top, while Lady GaGa’s ‘Alejandro’ jumps from 11 to eight to become her seventh US top ten hit.

Notable gains outside the top ten come from La Roux, who advances from 23 to 19 with ‘Bulletproof’, and Black Eyed Peas, who leap from 36 to 24 with ‘Rock That Body’.

The top ten singles in full (click where possible for our reviews):

1. (2) Usher ft. will.i.am: ‘OMG’
2. (-) Katy Perry ft. Snoop Dogg: ‘California Gurls’
3. (4) B.o.B ft. Hayley Williams: ‘Airplanes’
4. (3) B.o.B ft. Bruno Mars: ‘Nothin’ On You’
5. (4) Taio Cruz ft. Ludacris: ‘Break Your Heart’
6. (1) Eminem: ‘Not Afraid’
7. (8) Ke$ha: ‘Your Love Is My Drug’
8. (11) Lady GaGa: ‘Alejandro’
9. (6) Rihanna: ‘Rude Boy’
10. (7) Train: ‘Hey, Soul Sister’