Two years ago, the go-to "female empowerment" song for movies (The Devil Wears Prada's opening fashion-show montage) and TV shows (Ugly Betty, The Hills) was KT Tunstall's "Suddenly I See." In 2008, that honor has to go to Duffy's infectious tune about sexual freedom, "Mercy." Now the Welsh singer-songwriter is doing her best to avoid the trap of being known as just the "Mercy" girl — a tall order due to the fact that, well, "Mercy" is one hell of a catchy pop song. But judging from her performance last night at New York's Webster Hall, it looks like she's up to the challenge.

Opening with the torchy ballad "Syrup & Honey," Duffy took the stage wearing a slinky red belted dress with only her guitarist to accompany her. As her sultry vocals filled the room, I realized she should have told the rest of her band to stay home — not because they weren't good, but because Duffy doesn't deserve to have her voice drowned out by a full backing band. But since the band was there and ready to play, it made Duffy's rendition of "Rockferry," the title track off her debut album, that much more electrifying.

The roughly 45-minute set was comprised of all but one track from Rockferry, as well as a couple of new songs. The first new cut was the rollicking "Rain on Your Parade," which, while "Mercy"-esque in its overall sound and faithful to the "don't screw me around" theme of many of the songs from Rockferry, demonstrates how Duffy is moving away from her Sixties-influenced musical style and toward a more modern one (the synthesizer figures prominently).

Although it's obvious that Duffy has been taking performance cues from her fellow countrymen — channeling Roger Daltrey as she twirled her microphone, for example — she still hasn't quite learned yet what to do during a long guitar solo. But occasional looks of boredom aside, she engaged the audience throughout the evening, high-fiving fans, running to the side of the stage during "Hanging On Too Long" to grab a tissue (and apologizing for it! Those Brits, they're so polite!), and confessing that she tends to cry when she sings. Who could blame her? She even admitted that her songs were "depressing." Toward the end of the set I could have sworn I saw a tear in her eye, but then again it could have just been glitter.

And no, the concert would not have been complete without the crowd-pleaser "Mercy," along with a "hey!-in-case-you-haven't-noticed-this-is-the-big-single" light show. As soon as the familiar bass line intro came over the speakers, Duffy's tears were gone. She strutted across the stage with a sexy confidence gained only after having your song featured on Grey's Anatomy (could Gossip Girl be next?) and in the trailer for a Meg Ryan movie (you gotta start somewhere!) — and she brought the house down.