The 22-year-old star, who previously reached a chart high of four with her 2009 debut 'Tik Tok', zoomed to pole position after selling over 90,000 copies of her fifth release as a main artist. The song peaked at 95 in previous weeks based on downloads alone.
Meanwhile, two new entries grace the upper section of the chart this week, Chase & Status's 'Blind Faith' at five and 'Yeah 3x', the twelfth UK top 40 hit from R&B singer Chris Brown, at ten.
Elsewhere, positions 11-20 display risers aplenty, the most notable of which are Tinchy Stryder's 'Let It Rain', which is up 11 places from 25, album chart champion Adele and her 2008 ballad 'Make You Feel My Love', up four to 15, while Taio Cruz and Kylie Minogue's 'Higher' lifts 20 places to 17.
Just missing out on a spot in the upper half of the chart is Pink, whose 'Perfect' is a new entry at 21, while Aggro Santos and Kimberly Walsh prove to be the lone exception to the largely unchanged top ten, as 'Like U Like' plummets to 22 after debuting at eight last week.
The top ten in full:
1. (-) Ke$ha: 'We R Who We R'
2. (1) Bruno Mars: 'Grenade'
3. (2) Adele: 'Rolling In The Deep'
4. (4) Diddy-Dirty Money ft. Skylar Grey: 'Coming Home'
5. (-) Chase & Status ft. Liam Bailey: 'Blind Faith'
6. (3) Jessie J: 'Do It Like A Dude'
7. (5) Wretch 32 ft. L: 'Traktor'
8. (6) Britney Spears: 'Hold It Against Me'
9. (7) Rihanna ft. Drake: 'What's My Name?'
10. (-) Chris Brown: 'Yeah 3x'
Source: Official Charts Company
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