There was no upset scare this time for the Oceanside girls’ basketball team. The Mariners made sure of it.

Bailey Breen had 22 points and 15 rebounds, and Audrey Mackie added 14 points as the top-seeded and undefeated Mariners returned to the Class B South championship with an emphatic 49-20 victory over No. 4 Medomak Valley in the regional semifinals at the Portland Expo Tuesday.

Oceanside, the defending Class B champion, will play No. 2 Spruce Mountain in the final. The Mariners improved to 20-0, won their 53rd straight game and did so with ease, jumping to a 35-6 halftime lead in a game that looked nothing like their opener, a 54-48 victory over No. 8 Yarmouth in which they trailed for most of the first three quarters.

“We really wanted to get off to a good start,” Coach Matt Breen said. “That first game, you’ve got to give Yarmouth a lot of credit for what they did. They posed a lot of problems for us. … That was our big thing, try to get out to a good start early.”

The message was received as Oceanside looked every bit a juggernaut from the opening tip. The Mariners shot 65% (15-of-23) for the first half and scored 22 of the game’s first 24 points, with Breen (12 first-half points), Mackie (12) and Aubrey Hoose (seven) leading the surge.

“I think we just knew that we had to come out with intensity,” said Bailey Breen, a sophomore and Matt’s daughter. “I think it helped that we knew them, we had played them twice already this regular season, so we knew the personnel. But we did have to come out, play with high intensity and step on it from the get-go.”

Oceanside also clamped down on defense and, led by Breen and Abby Waterman (six points, 11 rebounds), outrebounded the Panthers, 44-31.

“The girls were focused. They were locked in,” Coach Breen said. “We hammered it in practice, we were not happy with the way we defended against Yarmouth. … We wanted to be really aggressive, moving our feet and just contesting everything.”

Addison McCormick had six points and Maya Cannon had nine rebounds to lead the Panthers (13-7), who advanced to the regional semifinals for the first time since 2011.

“At halftime, we were 10 percent from the field. … Turnovers were 8-5, rebounds were within three, so it was all right there. We just couldn’t score and they did,” Medomak Coach Ryan McNelly said. “When they shoot that well, there’s not much we can do.”