The charismatic rocker made it clear from the start of her brief, powerful set Saturday that her job was to fire the audience into a fever for the headlining act. To that end, she gave us her trademark headbanger girl routine, thrashing on her Flying V and flouncing on the stage like a toddler in a sandbox. When she opened her mouth wide, her voice soared on angel wings. Potter combines ragged hard rock and blues with a polished contemporary pop sound. It's like roadhouse glamor, the quintessence of blue-eyed soul. Her bandmates, as always, ripped it up on their best dirty-sweet tunes ("Sugar," "Nothing but the Water," "Paris"). Their joy was contagious. Potter and crew easily won over the mostly middle-aged audience members, who seemed to lose their minds when she kicked off her sparkly heels and bounced barefoot to an outsized take on the Jefferson Airplane classic, "White Rabbit." She dropped a sweet shout-out to a pair of honeymooners in the front row (whom she had met at her hotel), and signed a homemade Grace Potter & the Nocturnals banner for another couple, who looked like they were going to pee their pants in bliss.