Fleet Foxes, University of London Union, London

"Hello, we're U2!" yells one of the Fleet Foxes. "We're going to play all the hits." The crowd fall about laughing. It's a funny joke, but not that funny – and it's a neat reminder of how little the Seattle five-piece have to try tonight. Their acclaimed eponymous debut album of spooked, baroque Americana has only just been released, but it's won over ULU's sell-out crowd before the band even step on stage.

Indeed, the hype surrounding the group means that they've already outgrown the venue – it's quite clear that they could sell it out a few times over. Every vague, nervous little utterance from the band, every stilted pause to tune up, is met by lovestruck guffaws from the audience; we're sitting in the palms of their hands from the moment they step on stage. Or, at least, from the moment they launch into the woozy, hypnotic a cappella of "Sun Giant" (from the EP of the same name).

Fleet Foxes have the classic Seattle look down pat: long hair, check shirts and scruffy beards (apart from the guitarist Skye Skjelset, who looks about 16). But their spiritual home is California, not the city that grunge built. Their pastoral take on haunted folk-rock might sound as old as the Appalachian hills, but it's only as old as Crosby, Stills and Nash – their most obvious influence, and their only hindrance. Although Fleet Foxes are undoubtedly one of America's most brilliant new bands, their wilful nostalgia is the only thing that holds them back.

Still, they carry their retro aspirations with panache. Every song rings with a warm, rustic ecstasy. Live, the jangle- pop splendour of "Your Protector" comes alive with a Beach Boys-esque lightness, while "Ragged Wood" brims with rowdy harmonies.

As the band walk off stage, shouting "solo spot", lead singer Robin Pecknold gets a chance to flex his voice with a beautiful cover of Judee Sill's "Crayon Angels". Sill was the troubled junkie queen of the Laurel Canyon scene in 1970s Los Angeles – she moved in the same circles as Crosby, Stills and Nash, and died in near-obscurity. Pecknold manages to resurrect her ghost with his earnest, pitch-perfect interpretation of her gloomy folk song ("I sit here hoping for truth and a ride/To the other side"). It's a highlight of an already wonderful show.

Fleet Foxes may not quite have arrived in the 21st century, but with this much talent they'll get there in time.

The band tour the UK to 18 June ( www.myspace.com/fleetfoxes)