Welsh soul singer Duffy kept Leona Lewis from the UK's top spot in the charts with her hit Mercy, which went into its fourth week at number one.
X Factor winner Lewis entered the chart at number two with Sports Relief single Better in Time.
Duffy is also number one for the second week in the album chart with Rockferry while US rock band OneRepublic was the highest new entry at two, with Dreaming Out Loud.
In the singles chart, Dance act H Two O featuring Platnum dropped from two to three and OneRepublic stayed at four with Stop and Stare.
Nickelback's Rockstar remained in the top five, in its 18th week of release.
New entries included Panic At The Disco, Hard-Fi, Foals and Elbow.
Leona Lewis appeared in the singles chart several times twice for her double A-side track Footprints In The Sand, and again for former number one Bleeding Love, which re-entered the chart at 40.
Her album Spirit climbed from 12 to number four in the album chart, while Nickelback remained third with All The Right Reasons.
Other new albums in the Top 40 included Oracular Spectacular by MGMT at 12, The Very Best of Clannad at 20, and Superabundance by New Knives at 28.