One quick run in the first quarter gave No. 1 seed South Portland all the breathing room it needed. Add in tough defense throughout and the result was Thursday night’s 50-32 AA South semifinal win against No. 4 Bonny Eagle at the Cross Insurance Arena.

“It was a battle throughout the whole thing but we came out strong so I’m proud,” said South Portland’s 6-foot-10 junior center JP Estrella, who led all scorers with 14 points.

The Red Riots (19-1) will face No. 2 Thornton Academy (13-6) at 8:45 p.m. Saturday in the regional final. The teams split in the regular season. It is a rematch of the 2020 regional final, which saw Thornton knock off an unbeaten South Portland team in overtime.

The expected one-on-one battle between Estrella and Bonny Eagle’s 6-foot-8 Eliot Bouchard never really heated up. Both players found it tough to operate offensively against the other. Bouchard was held to six points on a tough shooting night, with Estrella playing behind and cutting off angles, allowing South Portland’s guards to sneak in and create several turnovers.

“That’s just kind of who we are. We have really good defensive guards,” said South Portland Coach Kevin Millington. “It’s sort of attack mode all the time and defensively we were tonight. We made it really hard for them to get inside the paint and (with) JP, it’s tough to be down in there when he’s there.”

South Portland had balanced scoring and multiple contributors. Jaelen Jackson added 13 points, Owen Maloney had 10 and reserve guards Jayden Kim and Ben Smith also chipped in and kept the pressure on Bonny Eagle, which shot 11 of 40 from the floor – and just 4 of 23 in the first half.

Aidan Walcott, Terrell Edwards and Hayden Campbell each scored eight points for the Scots (12-7).

“We just had a hard time holding on to the ball and finishing around the rim,” said Bonny Eagle Coach John Trull. “We picked a bad night to have our worst game.”

Kim (6 points) provided a spark for South Portland. A sophomore guard and probably the shortest player on the floor, he stole the ball and scored on a layup, then drove from the perimeter out of an offensive set for a scoop shot layup. That started an 11-0 surge that included a 3-pointer from Jackson as the Red Riots sprinted to a 13-4 lead.

“I came in kind of nervous because it’s the Civic Center, you know? I’ve never played here before,” Kim said. “But as soon as I got in, I was making plays and I just felt it.”

Bonny Eagle had the lead down to 14-9 at the first break thanks to a late 3-pointer by Campbell in the waning seconds off one of SP’s 10 first-half turnovers.

But the Scots shot 1 of 12 from the floor in the second quarter. South Portland wasn’t much better (4 of 14) but slowly stretched the lead to 24-13 at intermission.

When Bouchard made his first basket of the game late in the third quarter, the Scots were still in contact, down 32-22.

But Estrella stepped out and made a 3-pointer from the baseline and Jackson turned a steal near midcourt into a layup. South Portland’s lead maxed at 50-29 when Smith scored on a fast break off a nice touch pass from Estrella to cap a 12-3 fourth-quarter run.