SOUTH BERWICK — It was not enough that Thornton Academy entered Wednesday’s girls’ lacrosse playoff game as slight underdogs, but then the Trojans began in timid fashion, watching Marshwood take a five-goal halftime lead.

“We were a lot more motivated in the second half,” said Thornton sophomore Morgan Bolduc.

Bolduc capped the inspired Trojans’ comeback, scoring a free position shot with four seconds left in the first overtime to give fifth-seeded Thornton a 10-9 win over the No. 4 Eagles in a Class A South quarterfinal on Marshwood’s turf.

I think it was the overall mentality,” Trojans Coach Craig Agreste said of the comeback. “In the first half, we were reacting. They were the much more aggressive team.

“We talked about understanding the playoffs, and that the intensity picks up. They adjusted well.”

Bolduc paced Thornton with four goals. Izzy White and Grace Veroneau scored two apiece, and Hazel Stoddard and Abby Brown added one each. Stoddard’s goal came with 35 seconds left in regulation, sending the game into overtime.

Thornton (8-5) will play in the semifinals Friday against No. 1 Kennebunk (13-0). Marshwood is done at 9-4.

The Hawks have had a strong program under Coach Bernie Marvin (state champions in 2015) and came out fast, scoring 16 seconds into the game and again a minute later. Marshwood led 8-3 at halftime, but the Hawks’ thin roster proved costly in the heat and humidity, as Marshwood not only ran out of firepower but could not keep possession.

“We lost so many kids to injury. We had one sub, and the girls got gassed,” Marvin said. “Tribute to TA. They played hard.

“We got a lot of young kids out there and they got a taste of pressure lacrosse, which we didn’t get a lot of during the season.”

Marshwood senior tri-captains Ella Manero (three goals), Meagan Wentworth (two) and Natalie Singer (one goal, several steals) kept the Hawks in front, until the Trojans charged back.

“We had a lot more energy than in the first half,” Stoddard said.

Thornton began the second half with Brown scooping up a loose ball and scoring 47 seconds in.

The game went scoreless for almost the next nine minutes, until Thornton’s Mariposa Beane sprinted the length of the field before feeding White for a score. Two minutes later, Bolduc netted a tough-angle shot, and it was 8-6.

The teams traded goals, but that was all for Marshwood, as Trojan seniors Taylor Cormier and Bella Kalinyak led a charged defense, anchored by goalie Jazzmyn Goff.

Bolduc’s drive pulled Thornton within 9-8 with 5:51 remaining.

Marshwood had two possessions after that and lost the ball both times, the second turnover with 1:40 left. Thornton slowly set up its offense. Stoddard got the ball next to the net, zigged, then zagged, freeing herself for the tying goal.

“I caught it at the bottom of the crease, then I did a move around one girl and cut in front of the net,” Stoddard said.

In overtime, Bolduc had one free position shot blocked but was awarded another. She bounced it in.

“I thought, if I could get it low, it would get in.” Bolduc said.