Floral Park looked overmatched in the third set against South Side in Monday’s Nassau Class A girls volleyball semifinal. The Knights were the first to admit it.

“When we’re on, we’re on,” said outside hitter Grace Brandt. “But when we’re not . . . ”

Floral Park dropped the third set, 25-6. That left the Knights in a 2-1 hole, but it was one they were used to. Against the Cyclones in the season’s first match, they trailed 2-0 and came back to win. And they came back again with their season on the line.

The No. 3-seeded Knights triumphed, 23-25, 25-23, 6-25, 25-21, 25-15 and advanced to the county final against No. 1 Wantagh at 6:30 p.m. Wednesday at SUNY Old Westbury.

Senior twins Grace and Alice Brandt willed the team through rough stretches. Alice, the setter, had 28 assists and fueled a key rally in the second with a long serving run. Grace had 18 kills and came up with rally-stopping swings when needed.

After trading blows in the first and second sets, South Side (16-3) took what appeared to be a game-changing advantage in the third. Kiersten Colvin (13 kills, three aces) and Grace LaCava (10 assists, five kills) kept the Cyclones in the driver’s seat as Floral Park (15-3) struggled.

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But coach Lori Lorusso said the Knights have found themselves in this position before. She waited to call a timeout until 21-4, choosing to let the players work through the issue. That’s what she had done in the past.

“They have to figure it out,” Lorusso said. “I hate to prematurely call a timeout.”

Floral Park started slowly in the fourth set and trailed 8-0. Suddenly, however, the tide turned. The Brandts started clicking and their teammates followed suit.

Faith Balletta chipped in seven kills and three blocks. Natalie Hickman had six kills and three blocks.

“I thought in the fourth game we were going to lose,” Alice said. “Then when we were winning with 24 in the fourth set, I just got chills. I had a really good feeling.”

With momentum on their side, the Knights locked up an emotionally charged fifth set. They led from 4-3 and never looked back.

Now they’re one step closer to a county title. They belong on that court.

Wantagh holds off Lawrence. Despite dropping the second set to No. 4 Lawrence, Wantagh outlasted the Golden Tornado, 25-19, 25-27, 25-15, 25-20, to advance to the Nassau A final.

Lawrence’s ferocious pair of outside hitters, Kiara Stephens and Graciela Cruz, swung hard and swung often, but the Warriors’ back line — which included Jillian Graham, Christina Weir, Olivia D’Antonio, Abby Cullen and Emily Kaufmann throughout the match — responded late in the third and fourth games to seal the win.

“We worked really hard at staying in position and dedicated to our guard,” Graham said.