SOUTH BERWICK — Sophomore Leah Glidden wanted to find a way to honor her Marshwood High senior field hockey teammates Tuesday on Senior Night. So she gave them a win.

Glidden dove to tip in a shot by senior Hannah Costin just 29 seconds into overtime to lift Marshwood to a 1-0 victory over Thornton Academy in a pivotal Class A South game.

The victory likely secured the second seed in the upcoming playoffs for the Hawks, who finished the regular season 12-2.

“I’m a younger person on this team,” said Glidden. “We have a lot of seniors and they’ve been doing well the four years they’ve been here. Because it was their senior night, I honestly just wanted to go all out for them. They are amazing girls.

“So when that went in I was, ‘There you go.’ “

The Hawks controlled throughout, limiting the Trojans to four shots and four penalty corners. But Thornton, which finished the regular season 10-3-1, stayed in it because of its defense.

Goalie Isabella Capozzi made 10 saves, and Grace Decker and Sidney Hurst continually disrupted Marshwood rushes into the circle.

But the Hawks got the ball at the start of overtime and Glidden carried the ball right at Thornton.

“I definitely felt better in overtime with the girls,” said Marshwood Coach Lisa Truesdale. “They’re really smart with the ball, possessing the ball in space.”

Glidden got a call just inside the 25 and Costin took control, working a give-and-go with Elaine Bachelder. Costin pushed the ball into the circle to the right, then shot back across the goal. Glidden somehow got her stick on it and poked the ball inside the left post to end the game.

It ended so quickly, said Thornton Coach Lori Smith, “I don’t even know what happened.”

“Leah’s only a sophomore but I had her as a freshman last year and she’s calm,” said Truesdale. “She doesn’t frazzle easily. She’s been in this situation before. She’s got amazing speed and relentlessness so I wasn’t surprised that she tucked it through.”

It was a disappointing loss for the Trojans, who are the defending regional champs, but dropped to sixth place in the Heal point standings and will likely host a preliminary game on Saturday.

Smith spoke highly of Marshwood’s defense, which allowed only five goals all season and had 11 shutouts.

“They do a good job of stick block tackling,” she said. “That’s kind of their signature defensive play.”

The Trojans’ best chance may have come during a penalty corner with about 16 minutes remaining in the second half. Emma Dutremble took a hard shot from the top left of the circle, only to have Marshwood defender Madison Paulin block it with her stick.

“Our defense is stellar,” said Costin, one of the best players in the state. “It’s been awesome.”