Power punk affirmation from Yeah Yeah Yeahs

Rock is still best when served live -- as in vibrant, urgent, wild and free, the way singer Karen O of the Yeah Yeah Yeahs does it. On the first of two sold-out nights Saturday at the Henry Fonda Theatre, Ms. O and her two bandmates of New York punks erupted with a joy and intensity rarely matched on record or anywhere else.

The result was an ecstatic, unpredictable performance that tapped a vein of raw, original punk inspiration utterly lost on so much of the latest round of pop-punk hit-makers. The Yeah Yeah Yeahs are not mopey but vital, having emerged from the same New York garage scene that spawned the Strokes. They enjoyed a burst of media hype of their own even before the release of their debut album, 2003’s torrid “Fever to Hell.”

Karen O stepped onstage in tights and black gloves, looking not unlike a young Siouxsie Sioux with dark bangs over her eyes. She was edgily flamboyant, swinging her hair, her shoulders, her hips, marching in place and falling to the floor, feet up in the air. Guitarist Nick Zinner chopped out the minimalist riffs of “Black Tongue” frantically yet somehow nonchalantly, while the singer flailed and snarled blissfully.

Then came the lovesick pleading of “Maps,” a song now settling into heavy rotation on modern rock radio. It’s nice to hear the ravings of the Yeah Yeah Yeahs on the mainstream airwaves, but the band as it appeared at the Fonda could never be contained or even fully represented on the radio or on CD. They burned down the house.