As a music lover who grew up in the tiny Welsh coastal town of Nefyn, 23-year-old U.K. chart phenomenon Duffy admits she's still struggling to comprehend her sudden popularity. "There were more people in the South by Southwest [SXSW] audience [at my show] than there are in my town," says the former Aimee Duffy, whose hometown has a population of 2,550. "Three thousand people watched me at Stubb's."

Duffy is gearing up for her U.S. launch on the back of impressive sales at home. In the United Kingdom, her A&M/Polydor debut, "Rockferry," which marries her rich voice to a fresh take on classic soul and the '60s girl group sound, enjoyed the biggest first-week sales so far this year when it moved more than 180,000 copies after its March 3 release, according to the Official U.K. Charts Co. (OCC).

"That was mind-blowing," she says. "I'm not going to pretend it isn't strange. You really do have a new life overnight." In Europe, the positive reaction to the single "Mercy" at radio meant the scheduled April 7 release was brought forward, with "Rockferry" debuting at No. 2 in Holland, No. 3 in Denmark, and No. 7 in Switzerland, and going top 20 in Norway and Belgium.

In conversation, Duffy has a guileless quality that Bernard Butler, one of her producers and collaborators, attributes to her isolated Welsh upbringing. Nefyn was a bus ride away from the nearest record shop, which only stocked the top 40. That store has doubtless been doing good business with "Mercy," which spent five weeks atop the British chart. Now the upbeat, string-laden track is spearheading her U.S. campaign, where the album will be released this week via the relaunched Mercury imprint.