The Hawaiian-born musician, who recently lent his vocals to Travie McCoy's top five hit 'Billionaire', sold almost double that of 'Dynamite', leaving the former chart-topper in the runner-up spot on this week's chart.
Mars's arrival ends X Factor victor Alexandra Burke's two-week run at the top of the chart with Start Without You, which today drops four places to five.
The highest new entry this week is Must Be The Music winner Emma's Imagination, whose latest single 'Focus' makes it to seven and becomes her second Top 10 single this month after 'This Day'.
Also charting highly with a new release is Italian DJ Alex Gaudino, best known for 2007's 'Destination Calabria', who scrapes into the Top 10 with 'I'm In Love (I Wanna Do It)'.
Past the Top 10, three former number ones take a tumble down the charts, as Olly Murs's 'Please Don't Let Me Go' falls from five to 12, Flo Rida's 'Club Can't Handle Me' slips five spots to 14 and Yolanda Be Cool & D Cup settle in at 15 with 'We No Speak Americano'.
Nestling in between the fallers at 13 is a new entry from Enrique Iglesias and current X Factor judge Nicole Scherzinger entitled 'Heartbeat', while new Glee regular Charice makes her singles chart debut at 19 with 'Pyramid'.
The Top 10 in full:
1. (-) Bruno Mars: 'Just The Way You Are (Amazing)'
2. (2) Taio Cruz: 'Dynamite'
3. (3) Katy Perry: 'Teenage Dream'
4. (4) The Script: 'For The First Time'
5. (1) Alexandra Burke ft. Laza Morgan: 'Start Without You'
6. (6) Eminem ft. Rihanna: 'Love The Way You Lie'
7. (-) Emma's Imagination: 'Focus'
8. (8) Katy B: 'Katy On A Mission'
9. (10) Shontelle: 'Impossible'
10. (-) Alex Gaudino: 'I'm In Love (I Wanna Do It)'
Source: Official Charts Company
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