Rachel Platten, one of the hottest singer-songwriters around thanks to her hit "Fight Song," kicked off The Great South Bay Music Festival Thursday night as another sign of the event's growing power and popularity.

Long Island's biggest music festival, now in its ninth year in Patchogue's Shorefront Park, expanded to four days this year -- in part to accommodate the "Girls Night Out, Boys Can Come Too" tour headed by the "Bubbly" singer Colbie Caillat and the eclectic "Jar of Hearts" singer-songwriter Christina Perri, with Platten as the opener.

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However, "Fight Song," which crashed Billboard's Top 10 singles chart this week and has already topped the iTunes singles chart, loomed largest Thursday night. It generated a huge sing-along at the end of Platten's 25-minute set, with fans holding up signs stating what they want to fight for.

"To get to play to an incredible crowd like this is a dream come true," Platten said.

The eclectic festival continues Friday, with 311 headlining. Lotus and Chris Robinson Brotherhood will headline the daylong festivities Saturday, with Lou Gramm and Hot Tuna closing things out on Sunday.

Both Caillat, especially during the breezy "Brighter Than the Sun," and Perri, with her grand sing-along "Distance," were strong in their headlining sets Thursday, though Caillat's newfound love of Patchogue might have made a stronger impression.

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"This town is so cute," she said, adding that she had fun walking through the downtown with fiance Justin Young. "I want to look at property here."