The track, which entered the tally 18 weeks ago, holds off competition from Pink, who leaps 11 to two with 'F**kin' Perfect'.
Meanwhile, Pitbull and T-Pain's 'Hey Baby (Drop It To The Floor)' jumps from 10 to seven, while Far*East Movement and Ryan Tedder's 'Rocketeer' advances 16 to nine.
Further down the chart, Diddy-Dirty Money's 'Coming Home' climbs from 13 to 12, and Keri Hilson's 'Pretty Girl Rock' reaches a new peak on the chart, rising from 35 to 31.
Rihanna's 'S&M' vaults from 90 to 66, Adele's 'Rolling In The Deep' shifts from 84 to 69 and Ke$ha's 'Blow' re-enters at 96.
The top ten singles in full (click where possible for our reviews):
1. (1) Bruno Mars: 'Grenade'
2. (11) Pink: 'F**kin' Perfect'
3. (2) Katy Perry: 'Firework'
4. (3) Wiz Khalifa: 'Black And Yellow'
5. (4) Enrique Iglesias ft. Ludacris & DJ Frank E: 'Tonight (I'm Lovin' You)'
6. (5) Rihanna ft. Drake: 'What's My Name?'
7. (10) Pitbull ft. T-Pain: 'Hey Baby (Drop It To The Floor)'
8. (6) Britney Spears: 'Hold It Against Me'
9. (16) Far*East Movement ft. Ryan Tedder: Rocketeer'
10. (7) Ke$ha: 'We R Who We R'