On their last game on the field they’ve called home since they were in second grade, it was Madsen Madness Wednesday night at Centre Island Beach in Bayville.

Joe, the righthanded-shooting senior twin, scored five goals and Mike, the lefty, added four as Locust Valley clinched the Nassau IV league title and remained the only undefeated boys lacrosse team in Nassau County with a 13-8 victory over Seaford on Senior Night. Another senior, Tyler Liantonio, scored a goal and contributed five assists for the Falcons (7-0 in league, 14-0 overall).

“We all grew up down here, and when we wanted to hang out we’d say, ‘Let’s go to Centre Island,’ ’’ said Mike Madsen, who leads the team in scoring with 58 points (36 goals).

“This field used to have grass and rocks,” said Joe Madsen, who missed three games with injury but has scored 44 points (26 goals). “Fortunately, they put in turf.”

That suits the fast-paced style of the Falcons, who knocked off the previously unbeaten defending state champ, Cold Spring Harbor, Friday, 10-9. So does the convenient fact that one is a lefty and one is a righty.

“It plays nice to our offensive sets,” first-year coach Keith Cromwell said. “They are lacrosse rats. They are slick with the ball and have a unique way of working from behind the goal. When we really need a big play, we look to them.”

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The Madsens made big plays almost immediately after Dan Connell (four goals) gave Seaford (6-1 in league) the lead only seven seconds into the game. Less than a minute later, Joe Madsen picked up a loose ball in front and converted to ignite a 6-0 first-quarter blitz that set the tone.

Joe scored twice more in the first quarter on feeds from Liantonio (22 goals, 22 assists) while Mike Madsen scored a pair of unassisted goals in the period. “We’re pretty similar in skills,” Mike said. “Same things, opposite sides.”

That’s a mirror image opponents are tired of looking at. When Seaford scored two goals 1:04 apart in the third period to cut the deficit to 10-6, naturally it was a Madsen — Mike this time — who restored order when he scored in the slot on a feed from Liantonio, who fed Mike again to make it 13-6 early in the fourth.

The senior attack unit totaled 10 goals and six assists on a night when large banners with photos of all 16 Locust Valley seniors hung from the press box. “Whoever is in the right place at the right time” is how Mike Madsen described the team’s offensive mantra.

The twins hope to lead the Falcons on a long postseason run, but whenever that ends, their time playing together will not. Both committed to St. John’s.

“In the beginning, it wasn’t certain that we’d go to the same college,” Joe Madsen said. “But as the recruiting progressed, we both loved St. John’s. It’s a great fit.”

The Madsen Madness will continue.