Sam Petry stood at the plate, her season down to its final strike.

“I figured it might be my last senior at-bat, so I was definitely thinking I’ve got to just get a hit,” she said. “Just trying to put the ball on the ground and in play.”

Instead, she put it in the air and over the fence.

Petry crushed a two-out, two-strike, walk-off grand slam to lift No. 3 Island Trees to a 4-1 win over No. 6 Division on Saturday in the Nassau Class A softball quarterfinals.

“I’ve never seen her hit a ball that hard and that far in the four years she’s been on varsity,” said Island Trees coach Mike Bonsignore.

With the Bulldogs trailing 1-0, Hannah Vogt led off the bottom of the seventh with a single and advanced to third on a wild pitch. Vogt then beat the throw to third after a bunt by pinch-hitter Deanna Obremski to put runners on the corners. A walk to Kristin Grieshaber loaded the bases with no outs.

Division pitcher Justine Jean, who allowed four hits and struck out 11, induced a grounder for the first out. She struck out the next batter, leaving Island Trees down to its final out.

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Petry then drilled a 2-and-2 pitch to left, sending the Bulldogs into the semifinals, where they’ll play Clarke in a best-of-three series beginning Monday. When she reached home, she sought out Marissa Trezza, who had pitched brilliantly, allowing five hits, walking two, and striking out eight. She surrendered only a home run to Danielle Roselli in the fifth inning that put Division ahead, 1-0.

“I started crying in the seventh because I thought we were done,” Trezza said. “Two outs, two strikes. I put my head down and that was the second she hit it. She came home, came up to me, gave me a hug, and was like, ‘I got you, kid.’”

As Petry rounded the bases, she too was in tears.

“I was crying of joy,” she said. “I was so excited, so happy. I honestly didn’t think I could ever do that. But I just proved myself wrong.”