The Mount Desert Island High Schools girls soccer team had played most of the regular season without senior goalkeeper Sabine Costello-Sanders, who suffered a broken hand in the first game of the season and has since endured a strained knee ligament and a back issue.

But she has been back for five games and she posted her third straight playoff shutout on Saturday as the 10th-seeded Trojans upset the third-seeded Ellsworth High School Eagles 1-0 at Del Luce Stadium in Ellsworth.

Costello-Sanders “makes a big difference to our team,” said MDI coach May Chan, whose 7-10 team will now take on top seed and undefeated Hermon (16-0) in Wednesday’s 4 p.m. Class B North championship game at the Hampden Academy field.

Ellsworth, which had beaten its Hancock County rival twice during the regular season (4-1, 1-0), wound up 13-4.

Costello-Sanders made eight saves on 18 Eagle shot attempts including a win-preserving stop on dynamic striker Addi Laslie’s solo effort with 12:51 remaining in regulation.

 “She’s a very good goalie,” said Laslie, who has scored 28 goals this season and plays with  Costello-Sanders on their Dutch Soccer Academy club team in Warren.

Julie Mattson sent a perfect through ball to the speedy Laslie, who sprinted alone into the left side of the penalty area.

Costello-Sanders had come out to close down the angle and then took a quick step forward as Laslie prepared to shoot in order to be in position to smother the shot with her legs and body.

“I know [Laslie] really well. I tried to use my instincts,” said Costello-Sanders, who added that she waited until Laslie pushed the ball ahead a little too far before she rushed out to absorb the shot.

“It was a good save. I was trying to put it near the post,” said Laslie, who had six of Ellsworth’s 18 shot attempts.

Senior midfielder Lelia Weir scored the game’s only goal in the first half as her corner kick deflected directly into the net off the hands of Eagle goalkeeper Margarita Nadeau.

“It was an outswinger but I tried to put it as close to the goalie as I could,” Weir said.

It was a perfectly placed corner and Nadeau came down her goal line to try to swat the ball away with her hands only to have it glance into the side panel of the net.

It came with 17:32 left in the first half.

The tenacious Trojans turned in an exceptional first-half performance as they swarmed the ball and didn’t give the Eagles much time or space to generate offense.

They won the vast majority of the 50-50 balls which limited Ellsworth’s scoring chances.

The Eagles played with more energy and with more of a sense of urgency in the second half as they pressed for the equalizer.

They carried the play and had an 11-1 edge in shot attempts.

But MDI managed to get numbers behind the ball and get their legs and bodies in the way with Costello-Sanders coming up with saves when shots got through.

She made a couple of nice saves off long efforts taken by senior striker Paige Sawyer, one being a free kick. Sawyer also had a chance off a Tori Watkins corner that was snared by Costello-Sanders.

On another occasion, the ball pinballed in the MDI penalty area and Sawyer’s shot from the top of the penalty area was blocked by the defense.

Weir nearly gave her team some valuable breathing room with 14:34 left when her long free kick appeared as though it was going to nestle under the crossbar.

But freshman goalie Jayden Sullivan, who had replaced Nadeau, was able to elevate and direct the ball over the crossbar with her hands.

The talented Weir turned in an exemplary performance for the Trojans. Her well-placed corner kicks created scoring chances and she won a ton of balls all over the field.

Backs Kaleena Higgins and Hannah Ford did an exceptional job marking Laslie.

“She’s a great player so we focused on staying in front of her,” Higgins said.

Ford added that they also tried to deny her the ball.

“Their defense was really hard to get around,” Laslie said. “They definitely got numbers back [on defense]. They knew how to defend us.”

Weir said they played with more intensity than they have all year and Chan said she was proud of her team’s performance.

“Nobody is going to outwork us,” Chan said.

Laslie and Sawyer were constant threats for Ellsworth and Kiera Springer and Mattson were stout on defense.