Jukebox The Ghost took the XPoNential Festival’s Marina stage Sunday amid a cloud of heavy heat. The late-afternoon set had the muggy weather and an equally sluggish audience to contend with, but Jukebox’s brand of sunny piano pop prevailed, proving irresistible to even the most lethargic listeners. By the end of the show, a contingent of previously sedate spectators had taken up at the foot of the stage, dancing with whole-hearted enthusiasm.

As the members of Jukebox launched into their first song (“Good Day” from 2008’s Live And Let Ghosts) the crowd was restless, milling around or sitting on blankets and lawn chairs on the sloping hill, clutching water bottles with sweaty palms. As the tune wound down, singer and keyboardist Ben Thornewill’s chirpy voice cut through the haze: “Guys, check this out. To get to this show, he came from Kentucky, I came from Alaska, and he came from New York. So we’re really excited to be here.” People began to pay attention as the crowd swelled, and with the opening chords of “Empire” Jukebox was fully in command.

Along with the obvious charms of an energetic, hook-heavy sound, Thornewill’s and guitarist Tommy Siegel’s amiable, self-effacing banter won over a group mostly unfamiliar with their music. (Turning to her friend, one woman said, “I’ve never heard of them, but they’re great!”) Siegel discussed the pitfalls of Kentucky wedding attire in the summer: “I was…in a suit. So the sweat was private but it was there” and Thornewill prefaced the new song “Say When” by saying “It’s a dance song about how much I hate dance clubs.” (“That was an opportunity to boo, so we appreciate that,” Thornewill said after asking if they could play material from their upcoming record.) All three members of Jukebox The Ghost seemed happy to be there, all eager to convert a new cohort of fans—and just to have a good time.

With the jaunty and much-beloved “Hold It In” the band really hit their stride. A trio of girls by the sound tent stood up to shimmy and sing along. There were teenage boys chanting the words and one guy whistling and yelling, “You f–king rock, man!” Even the seated onlookers bobbed their heads, fanning themselves in time with the beat. Each sudden start and stop of the music found Thornewill flicking his wrists and bouncing. Jukebox’s fondness for the abrupt mid-song pause led to a lot of false-start applause, but their ability to snap without warning into and out of utter silence also showcased how polished and practiced they are.