Not even a torrential downpour could dampen the rocking spirit of the Great South Bay Music Festival’s opening night Thursday.

Long Island’s longest-running music festival celebrated its 10th anniversary at Shorefront Park in Patchogue with a rocking lineup that included an energetic set from headliners Third Eye Blind.

“All we have is right here and right now,” Third Eye Blind singer Stephan Jenkins told the crowd during a one-two punch of “Never Let You Go” and “Graduate.” “Let’s get some joy going.”

Brooklyn’s Kevin Devine, who was performing on the main stage as the storm closed in, said the impending downpour helped him focus his set. “It definitely made me think, ‘You better get your [act] together,” said Devine, who will release a new album this fall and rolled out fan faves like “Little Bulldozer” and “Bubblegum” in his half-hour set. “It made the show itself really fun.”

The four-day festival, which drew an estimated 4,000 fans Thursday night, runs through Sunday, when headliner Graham Nash will commemorate the festival’s 10th anniversary. Joe Nichols will headline the festival’s first country-themed night on Friday.

Thursday night was indie rock-focused, including a powerful set from Manchester Orchestra, who said they were introduced to the area by local heroes Brand New, and offered a grand version of “Pensacola.”

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This year’s festival also features an increased focus on charity.

For example, Long Island Cares, which will mark the 35th anniversary of the passing of the charity’s founder Harry Chapin on Saturday, will be manning the beer tents this year, with all tips going toward the group’s fight against hunger.

“It’s important to me and my daughter to give back,” said Festival co-founder and producer Jim Faith. “Mom instilled that in me. I’m an old ’60s guy, so that might have something to do with it.”