All the Mount Sinai girls lacrosse team has wanted to do is prove people wrong.

After winning last season’s state Class C championship, the Mustangs graduated a significant amount of talent. Naturally, they had their doubters entering this season. But after Sunday’s 7-5 win over Cold Spring Harbor in the Long Island Class C championship game at Stony Brook’s LaValle Stadium, there wasn’t a non-believer in sight.

“Since the beginning of the season, no one ever believed in us,” said Erica Shea, who was a force in the draw circle. “All we had was each other to look to. So we just wanted to prove people wrong and get back up there.”

There was no shortage of adversity in Mount Sinai’s path to the state tournament, especially against the Seahawks. The Mustangs were hit with multiple two-minute penalties, forcing them to play man-down for eight minutes.

But calm is contagious, according to coach Al Bertolone. His defense put nerves aside and set the tone, led by goalie Hannah Van Middelem. “Our defense was great,” said Bertolone, who specifically mentioned Emily Vengiglio’s work on Cold Spring Harbor’s Ashley Lynch. “When you play down for eight minutes , that says something about your goalie and your defense.”

Mount Sinai built a 3-0 lead in the first five minutes, with Camryn Harloff, Caroline Hoeg and Lean Nonnenmann scoring. Harloff netted her second of the game with 10:51 left in the first quarter for a 5-1 lead.

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Shea gave Mount Sinai (16-3) a 7-3 lead at the break on a score as time expired. But that was the Mustangs’ final goal, putting even more pressure on Van Middelem and the defense.

Sophia DeRosa scored with 19:42 remaining and Lynch scored with 1:41 left, but the Seahawks couldn’t finish the comeback. Van Middelem, who made five saves, helped limit the damage in a half in which Cold Spring Harbor (12-7) had possession a majority of the time.

“The kids persevered,” Bertolone said. “We didn’t lose our poise.”

The next stop for the Mustangs is SUNY Cortland, where they’ll face Honeoye Falls-Lima on Friday at 2:30 p.m. in the state semifinals.

And while the talent and depth of this Mustangs team now is evident, Van Middelem still has something to prove.

“No one has ever picked us to win,” she said, “so we just use that as motivation.”