When Wantagh allowed its first points of the playoffs on the first drive of the game and faced a deficit for the first time this season, the Warriors’ reaction wasn’t to put their heads down and sulk. Quite the opposite, actually. “We were encouraged,” coach Keith Sachs said.

“It was reassuring,” linebacker Sean Colbert said.

Wait, what?

“We lined up wrong four times. We lined up right once and they lost two yards. They completed a pass that we knew they’d never complete against us again,” Sachs said. “If they had been more physical than we were, that would’ve concerned me. Actually, I felt good about it.”

Or, as defensive back Jimmy Joyce said, “Time to start playing.”

The Warriors’ outlook only improved thereafter. Their Long Island-best defense took over in the second half Friday as Wantagh won the Long Island Class III championship by beating East Islip, 21-14, before a crowd of more than 5,000 at Hofstra’s Shuart Stadium.

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Wantagh (12-0) won the title for the first time since 2001 with a second-half shutout. East Islip finished 9-3.

“We came out flat. We weren’t in the right spots,” said Colbert, who had a huge interception at the Wantagh 2 late in the third quarter.

The Warriors were spot-on defensively after that first drive. “I’ve got all the pride in the world in our defense,’’ he said. “There’s no weakness 1-through-11.”

Wantagh bent on the first drive as East Islip moved 62 yards in 11 plays, including a 30-yard pass from Kyle Fleitman to Justin Orobello to the Wantagh 8 on third-and-8. Fleitman sneaked it in from the 1 and Doug Carpluk’s PAT made it 7-0.

Unfamiliar territory for Wantagh, which had recorded three straight shutouts in the playoffs, but not for long. The Warriors answered with an eight-play, 72-yard drive capped by Jake Castellano’s 30-yard touchdown pass to Tommy Rohan on an inside screen. Mike Piergiovanni’s PAT tied it at 7.

“We had to come back with a physical drive,” Sachs said.

Wantagh took a 14-7 lead after a one-handed interception by Joyce at the Wantagh 35 that he returned 19 yards. Eight plays and 46 yards later, Rohan scored from the 3.

“It was the second time they ran that play. They completed a pass the first time,” Joyce said. “I sprained my ankle during the week and couldn’t cut. Any other time, I would’ve intercepted the first one. I knew they would come back to it. I moved back a couple of steps and made a play.”

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East Islip did tie the score at 14-14 on Justin Taveras’ 13-yard run with 4:40 left in the half, but Wantagh again had an offensive answer.

Patrick Walsh returned the ensuing kickoff 85 yards for an apparent touchdown, but it was wiped out by a holding call. He still was credited with a 48-yard return to the Wantagh 47, and it took the Warriors just 2:14 to reach the end zone. Gavin Casey (70 yards, 12 carries) scored on a 1-yard dive for what proved to be the winning points.

Colbert (seven tackles), Casey (6 1⁄2), Anthony D’Onofrio (5 1⁄2), Jack LaVache (five) and Joe Valenti (five) were part of a unit that didn’t allow a point in the second half and finished the season having allowed 70 points, an average of 5.8 per game.

After a holding penalty nullified what appeared to be a 2-yard TD run by Taveras on first-and-goal, Colbert made a crucial interception at the 2 on third down with 43 seconds left in the third quarter to prevent the Redmen from tying it.

“We knew most of their stuff,” said Colbert, who jumped the route for the interception. “I saw the quarterback drop and I just broke on the ball. This defense had to step up and make plays a bunch of times in the second half, and we did it. There is no feeling like this in the world.”