OLD ORCHARD BEACH — When Dean Plante says he has a lot of faith in the young players on his Old Orchard Beach High girls basketball team, he isn’t kidding.

Three freshmen — guards Mackenzie Rague and Haley Plante and forward Abby Dubois — played huge roles Tuesday night as the fifth-ranked Seagulls held off No. 12 Monmouth 51-49 in a Western Class C preliminary round playoff game.

Plante led OOB with 15 points, hitting five 3-pointers; Rague directed the offense at point guard and hit a foul shot with 17.9 seconds left to give the Seagulls a seven-point lead and Dubois scored seven of her nine points in the final quarter.

“I was pleased with our composure, from start to finish, minus me,” said Plante. “Now we get a chance to run on the big floor against a familiar opponent.”

OOB (12-7) will play Western Maine Conference rival Traip Academy at 7 p.m. Tuesday in the regional quarterfinals at the Augusta Civic Center. Traip, ranked fourth, beat OOB twice in the regular season.

Monmouth finished 8-11.

This was a tight game throughout. The Seagulls held a one-point lead after one and the game was tied at 25 at the half.

But OOB scored the first four points of the third quarter on baskets by Anna Foss and Rague and never trailed again. A key factor was Plante’s decision to switch from a man-to-man defense to a 3-2 zone. That allowed his defenders to collapse on Monmouth’s Kristine Kahl, a gifted inside player.

She ended up with 12 points, but only four in the second half.

“That’s nothing new,” said Scott Wing, the coach of the Mustangs. “People have done that to her all year. And when that happens, it really makes it tough for us to score.”

Monmouth, he said, likes to keep the score in the 30s, low 40s at highest. “If it gets any higher, we’re usually in trouble,” he said.

Sophomore Kelsey Custeau hit a couple of 3-pointers in the third quarter — the under-sized Seagulls hit nine in the game — to help OOB to a 39-33 lead after three quarters.

Dubois (nine rebounds) provided much of the Seagulls’ offense in the fourth, splitting Monmouth’s defense to get crucial layups. And when Plante hit her fifth 3-pointer of the game with 3:27 left, OOB led 46-35.

Btu Monmouth kept fighting back. Melissa Brassard (14 points) had five points in a 7-2 run to cut the margin to six. And when a basket by Molly Menice with six seconds left was ruled a 3-pointer — despite her being two feet inside the arc — the Mustangs were within two at 51-49.

But they couldn’t complete the comeback.

Asked if they were nervous when Monmouth started coming back, OOB’s young guards — Rague and Plante — shook their heads.

“We just knew we had to play our game.” said Plante. “We couldn’t freak out over something like that.”

Added Rague, “Maybe I was nervous when the game started. There was a lot of pressure on us. But after the second quarter, I just got into the flow of the game.”

Christina Colman added 12 points for OOB, including a pair of 3-pointers in the second quarter.

“We came in with a game plan to play a zone because we knew they had a couple of shooters,” said Wing. “It became tough to defend when they started putting two shooters on the same side. Give them credit. They shot the ball well, which is what they had to do.”