His hit 'OMG' - a recent chart-topper in the US, Ireland and the UK too - fends off competition from B.o.B. and Katy Perry to notch up a sixth week at number one.
B.o.B. holds steady at two with 'Airplanes', a collaboration with Paramore singer Hayley Williams, while Perry sticks at three with 'California Gurls'.
'Ridin' Solo', the third single from US R&B singer Jason Derulo, advances from five to four.
Meanwhile, Gym Class Heroes frontman Travis McCoy leaps from 18 to nine with his debut solo single, 'Billionaire'.
Aussie pop five-piece Amy Meredith also enter the top ten this week, leaping from 35 to ten with 'Lying'.
The top ten singles in full (click where possible for our reviews):
1. (1) Usher ft. will.i.am: 'OMG'
2. (2) B.o.B. ft. Hayley Williams: 'Airplanes'
3. (3) Katy Perry ft. Snoop Dogg: 'California Gurls'
4. (5) Jason Derulo: 'Ridin' Solo'
5. (4) Yolanda Be Cool & DCup: 'We Speak No Americano'
6. (9) David Guetta & Chris Willis ft. Fergie & LMFAO: 'Gettin' Over You'
7. (7) Taio Cruz: 'Break Your Heart'
8. (6) Ke$ha: 'Your Love Is My Drug'
9. (18) Travis McCoy ft. Bruno Mars: 'Billionaire'
10. (35) Amy Meredith: 'Lying'