Israel Johnson invoked Southampton’s 70 percent rule, and that showed he was paying 100 percent attention during practice.

“The 70 percent rule is this,” professor/coach Herm Lamison said. “If a shot is taken from one side of the floor, there’s a 70 percent chance the rebound will come off on the other side. Izzy is a good student.”

Johnson, a slick 6-1 guard, earned a 100 on this fourth-quarter test. After a shot missed from the left side, he timed his jump perfectly from the right wing, caught the ball one-handed and artfully banked it home while drawing a foul. The three-point play with 4:59 left brought the crowd to life.

The spectacular play didn’t determine the outcome, as Southampton was well on its way to a 63-37 victory over Bridgehampton on Friday in a Suffolk B/CD boys basketball game at Suffolk County CC-Selden. But it showed that Johnson, the game’s high scorer with 16 points, hadn’t been daydreaming in practice.

“Coach stresses the 70-percent rule every day,” he said. “I was able to get into perfect position to rebound and score . . . If I was a little closer to the basket, I would’ve dunked it.”

That highlight notwithstanding, Southampton’s trapping defense confounded Bridgehampton and allowed the Mariners (15-6) to advance to the Suffolk small school championship game against Harborfields at 5 p.m. Tuesday at SCCC-Brentwood. They will face Oyster Bay in a state Class B regional semifinal at 8 p.m. on March 1 at SCCC-Selden. The Killer Bees (17-4) also will play March 1 at 3 p.m. at the same site against the Section IX winner in Class D.

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“It’s a fun game for bragging rights,” Johnson said of Friday’s contest, which matched neighboring communities. “We’re all friends off the court.”

Southampton’s Aaron Krzyzewski scored 13 points — seven in the first quarter as the Mariners built a 19-10 lead and six in the third, when a 20-7 burst blew it open.

“I had a lot of open shots thanks to my teammates,” Krzyzewski said. “Coach gives me the green light to shoot when I’m open, and he wants me to play more aggressively.”

And, of course, pay close attention in practice.