The Mount Sinai girls lacrosse team practiced hard, played with intensity and embraced the doubters.

And when the final horn went off in Tuesday afternoon’s Suffolk Class C championship at Dowling Sports Complex, there was no longer a reason to doubt the Mustangs.

The No. 2 Mustangs held previously undefeated Bayport-Blue Point to just one goal in the second half in a 6-5 upset win, and Hannah Van Middelem was at the center of it all.

The junior goalie made nine saves — not all of which were routine — and credited her defense for making things a bit easier.

“My defense just helped me a lot,” she said. “They channel outside shots, so it helps me see the ball well.”

It appeared as if Van Middelem saw shots before they even left the Phantoms’ sticks. She anticipated well and moved quickly. Coach Al Bertolone said she was the key.

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“If we were going to win, she had to have a big day,” he said. “And she did.”

Mt. Sinai (15-3) scored at 21:44 and 21:05 in the first half, taking a quick 2-0 lead. But the Phantoms closed the first on a 4-1 run with two goals apiece from Kerrigan Miller and Kelsi Lonigro.

Caroline Hoeg scored Mt. Sinai’s final goal in the first at 6:42. She scored again with 4:53 to play in the second after Rayna Sabella and Lean Nonnenmann opened the half with scores of their own.

There were five goal scorers for Mt. Sinai. Hoeg led the way with two tallies, and she said the Mustangs’ offensive depth has been a strength.

“We want to spread the wealth,” she said. “We want to spread the ball to everyone. We want everyone to have their own chances. It’s impossible to stop everyone.”

Erica Shea and Meghan Walker were nearly unstoppable on the draw, limiting Bayport to few opportunities in the second.

Julia Imbo scored the final tally for Bayport (17-1) with 41.6 seconds remaining.

Mt. Sinai will play on Sunday in the Long Island Class C championship at a site to be announced against the winner of Wednesday’s game between Cold Spring Harbor and Oyster Bay.