South Portland isn’t ready to give up its Class AA boys’ basketball crown yet.

The Red Riots, ranked second in the South, knocked off No. 1 Thornton Academy, 55-44, on Saturday night in the regional final at Cross Insurance Arena.

Jaelen Jackson, a senior guard and one of two starters back from last year’s championship team, led the way with 17 points, eight rebounds, five assists and four steals.

“Out of the gate, I hit a couple of buckets, and I always think I play better when I come out and hit some shots,” Jackson said. “Then I started getting attention, so I just wanted to get my teammates involved, and I think we all played a complete game. I don’t think there’s any way you beat a Thornton team – they’re very good – without everyone chipping in.”

Ben Smith added 11 points, Jayden Kim scored nine, and seven players scored for South Portland.

South Portland (18-3) will face North champion Portland (16-5) in the state final at 8:45 p.m. next Saturday at Cross Insurance Arena. South Portland beat Portland at the buzzer on a Jackson putback in the final game of the regular season.

“Whoever can hold the team to less points. It’s going to be a close one. That’s how (Portland Coach Joe) Russo coaches,” Jackson said. “I’m not expecting them to run and try to get 70 possessions in a game.”

The teams also have a Class AA finals history. They met in the first two championship games in 2016 and 2017, with Portland winning both, including an overtime decision at a nearly sold out CIA in 2016.

Thornton finishes its season 17-4.

South Portland led 22-18 at halftime and surged to a 37-21 lead in the first five minutes of the second half. Smith scored eight points in the third quarter. Jackson had five points and also dished out assists on 3-pointers by Smith and reserves Andrew Heffernan and Drew Folley.

“When (Jackson) is impacting the game in all phases – scoring, rebounding, assists and playing defense – he’s one of the best players in the state. I love the way he plays like tonight because he says, ‘I’m going to do everything,’ ” said South Portland Coach Kevin Millington. “He’s the engine that makes things go.”

South Portland was rolling and Thornton, less than 24 hours after its emotional win against Bonny Eagle capped by Will Davies’ debated buzzer beater, looked tired.

“We called a timeout and I could just tell. We were up like 15 and they were just kind of gassed,” Jackson said. “Obviously they had to play a lot harder against Bonny Eagle than we had to play against Scarborough (a 63-37 win), and I think that has an effect on this game, for sure.”

Thornton Coach Bob Davies said, “In the third quarter, they got the better of us. The big part of it is missed shots and we turned the ball over a couple times. The other part is we played defense well and then didn’t close out the defensive possession and didn’t get the rebounds.”

Will Davies led Thornton to two regular-season wins against South Portland. He had 30 points in a 69-60 win at South Portland, and 26 points with 11 assists in an 82-61 win in Saco. This time, though, the returning Varsity Maine all-state player had a hard time finding space, scoring nine of his team-high 15 points at the free-throw line. His first basket came with 2:38 left in the third quarter after South Portland had surged to a 37-21 lead following a Smith 3-point play.

“We knew we had to come out with really good energy,” said Smith, one of several players who took turns guarding Davies. “Especially guarding Will, that good of a player, we just have to outwork him and make him have to go up and down the court all game, and that’s what we did, I feel.”

Braden Camire scored 14 points for Thornton.

“It’s definitely hard to beat those guys three times in a year. We didn’t do it,” Bob Davies said.