Throwing his guitar and jacket to the ground in the squealing wreckage of Devil's Haircut, Beck Hansen storms off stage after just one song. For a moment it looks as if his revival is derailed, the show a write-off, all concerns confirmed. After all, alt-pop's master assimilator – the doe-eyed LA dropout who built a formidable name by amalgamating blaxploitation soul, hip-hop turntablism, slacker-rock ennui, electropop, psych-country and the funk showman moves of James Brown and Prince – is only recently back from the brink. A spinal injury on the video shoot for E-Pro in 2005 hobbled his touring career, and following 2008's Modern Guilt he withdrew into soundtracks, production and label projects. When his first release in four years was 2012's Song Reader, a book of sheet music for other acts to perform, he seemed to have journeyed all the way into the esoteric art hinterland, never to return.

Within seconds, though, he's back, instrument issues resolved, side-sliding into the funk-rock firestorm of Black Tambourine with one eye on the Kate Bush comeback dollar. "This is our first London show in about 70 years," he vastly overestimates, but certainly the past five have seen only sporadic sightings and nothing as full-on as this iTunes festival takedown. With every song powered by brutal riffs that suggest Beck's radar has subconsciously picked up Royal Blood, he throws himself into a languid Loser, the mechanised funk of Hell Yes and the frenzied harmonica hoedown of Novacane with a rubber-limbed litheness that must be a miracle of orthopaedics. Beck may not be able to mimic James Brown's splits any more, but bassist Justin Meldal-Johnsen makes up for it, throwing himself at speaker stacks and moonwalking with abandon.

Beck's return was heralded with the acoustic-led Morning Phase in February, a warmup for a more lively companion album to come and a sister piece to his acclaimed 2002 breakup record Sea Change. They're both affecting listens, but when he follows a snippet of Donna Summer's I Feel Love with 15 minutes of country rock (Blue Moon) and songs resembling the Byrds in a tube tunnel (Heart Is a Drum), it's disheartening that an artist this exploratory would mature down the standard rootsy routes.

So it's a relief when the arcade machine noises and tin-can vocals kick in again and the filthy party pop of E-Pro finds the guitarists moshing themselves to the ground, their bodies dragged off as Beck wraps the stage in police tape. They quickly contaminate the scene with an encore of Sexx Laws, Beck's ardent impression of a malnourished Barry White on Debra and a lengthy Where It's At, featuring snippets of so many 70s disco classics it's as if they've hacked Nile Rodgers' iCloud. A ramshackle reboot of the classic soul revue, then, and Beck remains its consummate showman.