The 22-year-old, who in January was crowned the BBC's Sound Of 2011, rocketed straight to the top of the chart after taking the unconventional move of releasing her latest track to radio and retail on the same day.
The song's success also gives featured artist B.o.B his third UK chart-topper, following last year's 'Nothin' On You' and 'Airplanes'.
The second-highest new entry this week belongs to Enrique Iglesias, who scores his ninth UK top ten hit with Ludacris collaboration 'Tonight (I'm Loving You)' at five.
Jessie J also occupies a second spot in the top ten with her first single 'Do It Like A Dude', which drops one place to seven. The song made a somewhat underwhelming debut at 25 upon its release in November 2010, but has since reached a peak of two and clocked up sales of over 300,000 copies.
Just behind Jessie J are Taio Cruz and Kylie Minogue, who jump to eight from last week's 17 with 'Higher', while Chase & Status round out the top ten after falling five places with 'Blind Faith'.
In the double digits, Pink and Tinie Tempah both celebrate massive advances up the rankings, as their respective tracks 'F**kin' Perfect' and 'Wonderman' gain ten and 26 spots to become this week's 11 and 14.
Rihanna manages to place three songs in the second quarter of the chart, as her former number one 'What's My Name?' at 15 and David Guetta team-up 'Who's That Chick?' at 16 are joined by her new release 'S&M', which rides the tide of controversy caused by its music video to this week's 20.
The top ten in full:
1. (-) Jessie J ft. B.o.B: 'Price Tag'
2. (2) Bruno Mars: 'Grenade'
3. (1) Ke$ha: 'We R Who We R'
4. (3) Adele: 'Rolling In The Deep'
5. (-) Enrique Iglesias ft. Ludacris: 'Tonight (I'm Loving You)'
6. (4) Diddy-Dirty Money ft. Skylar Grey: 'Coming Home'
7. (6) Jessie J: 'Do It Like A Dude'
8. (17) Taio Cruz ft. Kylie Minogue: 'Higher'
9. (10) Chris Brown: 'Yeah 3x'
10. (5) Chase & Status ft. Liam Bailey: 'Blind Faith'
Source: Official Charts Company
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