Soul singer Duffy, who was the runner-up in the BBC's Sound of 2008 search for new talent, has topped the UK singles chart for a second week.
The rising Welsh star entered the chart at number one last week with Mercy.
H Two O featuring Platnum's What's It Gonna Be rose five places to number two, pushing Canadian band Nickelback from second place to third.
Join With Us by The Feeling went in at number one in the album chart, while Amy Winehouse is at number three.
The troubled singer, who has recently performed at the Brit Awards and won five Grammys, was at number 14 last week but her recent successes have boosted her sales.
UK SINGLES CHART
Nickelback stayed at number two in the album chart with All the Right Reasons.
Jack Johnson, who topped the album chart last week with Sleep Through the Static, was down to number eight, while Michael Jackson's Thriller 25, the 25th anniversary reissue of his iconic album, was down three places to number six.
Former G4 tenor Jonathan Ansell's solo debut, Tenor at the Movies, was at number nine.
UK ALBUM CHART
Back in the singles chart, the BBC's Sound of 2008 winner Adele's Chasing Pavements fell one place from five to six, while David Jordan's Sun Goes Down was down three to seven.
Brit winner Mark Ronson was up from 22 to 13 with Valerie, featuring Amy Winehouse.
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