Music
The R&B singer holds off competition from Rihanna's 'Rude Boy', which leaps six places to two.
Iyaz drops one place to three with 'Replay', while Owl City and The Midnight Beast hold steady in the top five.
Lady GaGa and Beyoncé collaboration 'Telephone' climbs nine places to eight, while Cheryl Cole drops two to 11 with '3 Words'.
Elsewhere, Gabriella Cilmi's 'On A Mission' drops five places to 21 and Train score the highest new entry at 16 with 'Hey, Soul Sister'.
The top ten singles in full (click where possible for our reviews):
1. (1) Jason Derulo: 'In My Head'
2. (8) Rihanna: 'Rude Boy'
3. (2) Iyaz: 'Replay'
4. (4) Owl City: 'Fireflies'
5. (5) The Midnight Beast: 'Tik Tok (Parody)'
6. (6) David Guetta ft. Kid Cudi: 'Memories'
7. (3) Taylor Swift: 'Today Was A Fairytale'
8. (17) Lady GaGa ft. Beyoncé: 'Telephone'
9. (7) Ke$ha ft. 3OH!3: 'Blah Blah Blah'
10. (10) Jay Sean ft. Sean Paul, Lil Jon: 'Do You Remember?'
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