Bobby Hegarty had some serious rhythm.

The senior righthander worked quickly and economically while throwing his third straight postseason one-hitter to lead Wantagh past Mount Sinai, 3-1, on Saturday in the Long Island Class A baseball championship game before a crowd of more than 1,100 at the Police Athletic League Complex in Holtsville.

It was the Warriors’ third Long Island baseball championship under coach Keith Sachs and first since 2010. Wantagh (24-5) will meet the winner of Queensbury and Christian Brothers Academy in a state Class A semifinal on Saturday in Binghamton.

“It was vintage Hegarty,” Sachs said. “He gives a batter a millisecond of time between pitches and then he brings it. It’s sexy when a pitcher can pound the strike zone and make it fun to play defense behind a guy who [is] a strike machine.”

Hegarty, who gave up a line-drive single to Mount Sinai catcher George Rainer in the third inning, allowed only three baserunners, two on infield errors. He walked none and struck out two. He threw 19 first-pitch strikes to 23 batters and finished with 54 strikes in 71 pitches.

“I was hitting my spots and pitching to contact,” said Hegarty (7-3), a member of what is considered the best three-man rotation on Long Island.

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Hegarty poured it into the strike zone and made quick work of the Mount Sinai offense. On the other side was West Virginia-bound Sam Kessler, who was undone by poor defense. He allowed five hits and three unearned runs with seven strikeouts and one walk.

Wantagh took advantage of an infield error to score twice in the third inning for a 2-0 lead. Kessler retired six of the first seven batters through two innings, but in the third, John Conroy reached on an infield error and advanced to second on a one-out single by Anthony D’Onofrio. Jimmy Joyce singled to load the bases before Will O’Brien drilled a long fly ball to leftfield for a sacrifice fly and a 1-0 lead. Anthony Fontana followed with a clutch RBI single to make it 2-0.

Mount Sinai responded with an unearned run in the bottom of the third. Jake Golino reached on an infield error before Rainer laced a single to left. Golino scored to make it 2-1 when DJ Gatz grounded to short and the throw to first got away.

From there, it was all Hegarty. He retired the final 13 batters and benefited from a beautiful running catch in foul territory by catcher Trevor Fagan to start the seventh.

“It was a great day,” said Hegarty, who will play for the University of Scranton in the fall. “Our fans were out in full force and in support of our team and it was an exciting day for Wantagh baseball.”

Hegarty, who allowed only one hit in previous playoff wins over Garden City and North Shore, was swarmed on the mound after the final groundout.

“This is a very close group,” Wantagh assistant Mike Ninivaggi said. “They do everything together and they’ve worked hard all offseason to be here. What a wonderful win, made easier, of course, by Hegarty

.”