The 22-year-old holds off the Black Eyed Peas's 'Imme Be', which climbs two places from last week's four.
Lady Antebellum, who debuted at number one on the US Billboard 200 with their second album Need You Now last week, rise five places to three with the LP's title track.
Young Money drops one place to four with 'BedRock', while Lady GaGa's 'Bad Romance', which has so far peaked at number two, falls five places to six.
Black Eyed Peas jump seven places to nine with 'I Gotta Feeling', which spent 14 weeks at number one last year.
Elsewhere, Jason Derulo's 'In My Head' climbs three places to 11, while Rihanna drops three to 13 with 'Hard'.
Pink secures the highest new entry at 18 with 'Glitter In The Air'.
The top ten singles in full (click for our reviews):
1. (1) Ke$ha: 'Tik Tok'
2. (4) Black Eyed Peas: 'Imme Be'
3. (8) Lady Antebellum: 'Need You Now'
4. (3) Young Money: 'BedRock'
5. (2) Lady GaGa: 'Bad Romance'
6. (5) David Guetta ft. Akon: 'Sexy Bitch'
7. (9) Train: 'Hey, Soul Sister'
8. (6) Ludacris: 'How Low'
9. (16) Black Eyed Peas: 'I Gotta Feeling'
10. (7) Iyaz: 'Replay'