The postgame singing was jarringly off-key. But the second-half performance was on point and well-orchestrated.

With quarterback Michael Proios conducting, and a variety of players joining the chorus, Mepham rallied to defeat host Carey, 42-27, Thursday in a Nassau II showdown of unbeaten teams.

The Pirates (4-0) were in perfect harmony as they scored 28 consecutive points to erase a 20-14 deficit. That made the team’s “Happy Birthday” serenade to coach Anthony Cracco sound sweet.

“We haven’t beaten Carey since 2011. It’s a great team and a great program,” Cracco said. “We made mistakes and get away from playing our game in the first half. But then we picked up the pace and got a lot of guys involved. That was a key to the second half.”

Mepham marched 62 yards in eight plays on its first possession after the break. More telling: The drive took only 2:43. The pace was quick and so were the players. Proios, who was 11-for-14 for 124 yards and two touchdowns in the second half, hit Anthony Novello on three straight passes covering 31 yards and Michael Estevez punched it in from the 1 for the first of his two touchdowns to put the Pirates ahead for good at 21-20 after Kevin McCleneghan’s point-after kick.

The Pirates made it 28-20 with a six-play, 55-yard drive that took just 3:14. A spinning, tackle-breaking 18-yard run by Nah’jel Sands set up Proios for a 17-yard TD pass to Novello on a quick screen.

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Carey quarterback Dominic Rutigliano, who had three TD passes, was flushed from the pocket on the next series and hit hard on the scramble. He fumbled and linebacker Matt Hegi recovered at the Seahawks’ 20. Three plays later, Estevez scored from the 3.

The game got away from Carey (3-1) on the next sequence when Kenny Franquiz recovered a fumbled kickoff on the Seahawks’ 35. The Pirates capitalized again, with Proios showing some wizardry by faking left and then throwing a screen to the right that Jack Gibbons took 31 yards for a touchdown and a 42-20 lead early in the fourth quarter.

Carey made it a two-score game on a 36-yard TD pass from Rutigliano to Riley DeMeo, who also kicked a 42-yard field goal on the last play of the first half. But the Pirates made sure there would be no comeback with a clock-killing drive that pinned Carey deep and a strong pass rush on Rutigliano.

The screen pass was an effective weapon all game for Proios, who thrived when the pace quickened and moved the ball around like a basketball point guard.

“I definitely like a fast pace. I love leaving the pocket and throwing on the run. Pocket passes are not my favorite,” Proios said. “When we’re snapping it fast and hitting different guys, they don’t know where I’m going to. We like to wear defenses down and I think they were a little tired in the second half.”

Cracco called his quarterback “an elite player, one of the best in Nassau County. He’s a three-year starter and he always leads us in the second half. He’s got ice water in his veins and gets better as the game goes on.”

Which added some icing to Cracco’s birthday cake.