SACO – Here was the challenge for the Thornton Academy girls: From the opening tip, play as hard as you can for as long as you can.

You got it, coach.

The Trojans rode a frenetic half-court defense and a balanced attack Wednesday night to cruise past South Portland 50-30 in a Western Class A preliminary-round girls’ basketball playoff game at Thornton Academy.

Sixth-seeded Thornton Academy (11-8) next plays No. 3 Marshwood (15-3) in a regional quarterfinal at 2 p.m. Monday at the Portland Expo.

Olivia Shaw led the Trojans with 13 points, six rebounds and three steals. Jordan Agger had 11 points and four rebounds. Meghan Agger had nine points and six rebounds.

Brianne Maloney had six points and seven rebounds, and Libby Grant added six points for No. 11-seed South Portland (7-12).

“The girls responded to the challenge right from the start,” said Thornton Academy Coach Eric Marston. “We were denying off the ball pretty well and we were able to get some easy baskets going the other way, which is what we were hoping to do.”

Jill Legere hit a jump shot from 18 feet 1:15 into the first quarter to give South Portland its only lead, 2-0. The Trojans then went on a 10-0 run to close the quarter. The Red Riots never recovered.

“We had some early opportunities to score, made some mistakes early turning the ball over and their defense spelled doom for us tonight,” said South Portland Coach Mike Giordano. “You really have to make them play the whole half court and we didn’t do a good job of that.”

South Portland played some pretty tough defense as well, led by Maloney, Maryalice Gurnee and Danica Gleason. The Red Riots held the Trojans to just nine points in the second quarter, scoring eight to go into halftime trailing, 19-10.

Thornton started clicking in the third as the Agger sisters, Tori Lands and Kaitlyn McCrum each scored four points to outscore the Riots 19-11 and open a 38-21 lead.

“They were trying to clog the post,” said guard Kaitlyn McCrum. “But we reversed the ball a lot and got it inside. After a while you figure out what’s working and what’s not. We started clicking.”

After that, the Trojans’ defense took over.

“The kids battled the whole way,” Giordano said. “We didn’t have very many easy games (this season) and they competed every night. Tonight, they competed until that last horn went off and I’m really proud of them.”

Looking ahead, Marshwood presents its own challenges to the Trojans. The Hawks beat them 45-36 on Jan. 10.