Faced with a halftime deficit for the first time this season, the Baldwin girls basketball team leaned on its defensive intensity to earn its fourth consecutive Nassau Class AA title.

Kaia Harrison’s three-pointer with 5:42 left in the fourth quarter put top-seeded Baldwin up by eight points and gave the Bruins enough breathing room to withstand the pressure of second-seeded Massapequa in a 37-29 victory Saturday at Hofstra’s Mack Sports Complex.

Baldwin put increased emphasis on its signature full-court press at halftime, leading to a flurry of steals, traps and rushed possessions by Massapequa (16-6). Baldwin opened the third quarter on a 9-0 run after trailing 19-18 at the break.

Baldwin coach Tom Catapano’s pep talk helped.

“They kind of played a triangle-and-two, so he told us when we went inside, just keep being aggressive and don’t put your head down; don’t give up or anything,” said Harrison, who had 10 points.

Said Catapano, “I told them at halftime, ‘There’s no tomorrow. If we don’t get this done in the next 16 minutes, our season’s over.’ ”

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Aziah Hudson started the game-changing 9-0 run with a layup off an assist from Jenna Annecchiarico. Sarah Pulis and Harrison followed that up with baskets of their own. Montia Moon (eight points) capped the run with a three-pointer, putting the Bruins up 27-19 with 2:52 left in the third quarter.

Kathleen Doherty (nine points) and Gabriella Heimbauer (10 points) put Massapequa within four at 27-23 at the end of the quarter. The Chiefs closed to within four again with 21.7 seconds left on a free throw from Doherty, but Pulis and Nadia Elcock made all four of their free-throw attempts after that, sealing the seventh county title in eight years for Baldwin (18-1).

“They played great,” Massapequa coach Billy Herr said of his team. “Who’s played them that close this year in the county? We’re going to be back next year even better. My girls, I couldn’t ask for more. We got a little nervous in the third quarter. We came back, they kept going, got out of our game a little bit. But our defense never stopped.”

The Chiefs’ lead at halftime represented something that not even four-time defending state champion Ossining could do. Baldwin put a screeching halt to Ossining’s winning streak against New York opponents that dated to March 2012 with an 83-73 win on Dec. 28.

Baldwin will face Central Islip in the Long Island championship game at 2:30 p.m. on March 11 at SUNY Old Westbury. Baldwin lost in the game each of the previous two seasons, but Annecchiarico said the Bruins are “hungry.”

“We want it. We definitely want it,” she said. “The last two years, nothing fell for us.”

A start like the one against Massapequa wouldn’t be a good idea against a fast Central Islip team, but Catapano has faith in his players.

“I’m just proud of our kids because we found a way to win when we didn’t play our best basketball,’’ he said, “and that’s the sign of a really good team.’’