Southampton’s Timmy Alejo had just three points after three quarters.

“Timmy wasn’t playing his usual good game for us,” Mariners boys basketball coach Herm Lamison said.

But Alejo came up clutch when it mattered in the fourth quarter.

The Mariners’ senior forward got a key rebound on a missed free throw and was fouled. He calmly hit two free throws with 11.1 seconds left as Southampton outlasted Center Moriches, 74-71, Tuesday night before a crowd of 700 at the Suffolk Class ABCD boys basketball final at Suffolk CCC-Brentwood.

Center Moriches’ Sean Braithwaite, who had 21 points and seven rebounds, missed a tying attempt that hit the backboard from two-thirds court at the buzzer.

Southampton (20-2) faces the winner of the AA final between Bay Shore and Half Hollow Hills East on Sunday (7:30 p.m.) at Suffolk CCC-Selden for the Suffolk overall championship.

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“We were in Timmy’s ear to give us something,” Lamison said. “He delivered with that big rebound and two clutch free throws.”

Center Moriches (19-4) took its largest lead of the game, 62-57, with 5:23 remaining in the fourth quarter after back-to-back three-pointers by Troy Goode and Tyiquon Nix, who had a game-high 23 points.

But Southampton scored 15 of the next 23 points and led 72-70 after a three-pointer by Andre Franklin (17 points). Aaron Krzyzewski knocked away a back-door pass intended for Braithwaite with 22.9 seconds left.

Krzyzewski, who had 14 points and six rebounds, was fouled but missed both free throws with 13.3 seconds left. However, Alejo (who had nine of his 12 points in the fourth quarter) skied from the right side of the free-throw line, tracked the ball to his left and was fouled with 11.1 seconds to go.

“We have a play for that on free throws and it happened to work,” said Alejo, who had a bloody jersey and had to change his uniform top in the second half.

Alejo’s free throws made it 74-70. Braithwaite was fouled on a three-point attempt with 5.3 seconds remaining. He made the first shot, but missed the second. He intentionally missed the third, but Center Moriches was called for a lane violation.

Southampton’s Micah Snowden (16 points, 10 rebounds) missed both free-throw attempts after he was fouled with four seconds to go, but Braithwaite’s prayer could not find iron.

Center Moriches plays Oyster Bay in the Long Island Class B final on Tuesday (7:30 p.m.) at SUNY-Old Westbury. Meanwhile, Southampton meets a team to be determined in the Long Island Class A final on Sunday, March 12 (11 a.m.) at Stony Brook University.

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“This win,” Lamison said, “is a major accomplishment for us.”