The track is her seventh chart topper in the UK if including her tracks as a featured artist.
Psy drops one place from last week's top spot to two with his worldwide smash 'Gangnam Style'.
One Direction land at three with their brand new single 'Live While We're Young', having been number one in the midweek chart.
Adele lands at four with her James Bond theme 'Skyfall', despite its sales only counting for two days since its release on Friday (October 5).
Ellie Goulding scores a top five hit with new single 'Anything Could Happen' at five.
The Script and will.i.am drop four to six with 'Hall of Fame', while Flo Rida also falls four to seven with 'I Cry'.
David Guetta and Sia are a non-mover at eight with 'She Wolf (Falling to Pieces)', while Conor Maynard stays level at nine with 'Turn Around'. Taylor Swift falls six at ten with 'We Are Never Ever Getting Back Together'.
Jason Mraz rises 12 places to 11 with his 2011 hit 'I Won't Give Up', following appearances on The X Factor.
Nicki Minaj secures a new entry at 20 with her latest single 'Va Va Voom', while Taylor Swift scores another entry at 26 with 'Red'.
Kanye West rises eight places to 30 with his Jay-Z and Big Sean collaboration 'Clique'.
The Other Tribe enter at 36 with new track 'Skirts', while Adele's live performance of 'I Can't Make You Love Me' is a new entry at 37.
Listen to Rihanna's 'Diamonds' below:
Source: Official Charts Company
> This week's albums chart