Bruno Mars climbs to two with 'Just The Way You Are', while Taio Cruz falls to three with his former chart-topper 'Dynamite'.
Meanwhile, US newcomer Mike Posner leaps from eight to four with his debut single 'Cooler Than Me'.
Cee Lo Green also makes good progress this week, advancing from nine to five with 'F**k You', which debuted at number one on the UK singles chart yesterday.
The only new track in the Top 10 comes from Nelly, who jumps from 13 to eight with 'Just A Dream' to score his first Top 10 hit Down Under since 2004.
The top ten singles in full (click where possible for our reviews):
1. (1) Rihanna: 'Only Girl (In The World)'
2. (3) Bruno Mars: 'Just The Way You Are'
3. (2) Taio Cruz: 'Dynamite'
4. (-) Mike Posner: 'Cooler Than Me'
5. (9) Cee Lo Green: 'F**k You'
6. (5) B.o.B. ft. Rivers Cuomo: 'Magic'
7. (7) Katy Perry: 'Teenage Dream'
8. (13) Nelly: 'Just A Dream'
9. (6) Usher ft. Pitbull: 'DJ Got Us Fallin' In Love'
10. (10) Eminem ft. Rihanna: 'Love The Way You Lie'