SOUTH PORTLAND — A misplay opened the door.

Thornton Academy barged through with six unearned runs in the second inning and went on to beat defending state champion South Portland, 6-4, Tuesday at Wainwright Sports Complex in a game between two of Class A South’s top teams.

“This win helps a lot. Everyone wanted to win. Everyone was hyped,” said Josh Kopetski, Thornton’s junior lefty who improved to 3-0 with his six-inning, seven-hit, four-run (two earned) effort.

Thornton, ranked first in the Heal points, improved to 7-1. South Portland (6-2) entered the game No. 4 in the competitive division and has lost two straight.

“I’m pleased with the effort. The kids are competitors. That was a good high school baseball game,” said South Portland Coach Mike Owens. “We just need to clean up a few things so the results are better, too.”

All of the runs in the game were tainted.

South Portland got to Kopetski for two runs on three hits in the first inning, aided by two uncharacteristic passed balls by senior catcher Nic Frink. The second passed ball allowed Andrew Heffernan (2 for 3) to score from third and moved Nolan Hobbs into second. Hobbs scored on a solid single to right by Ryan Thurber.

In the second inning, South Portland starter Hobbs (four innings, five hits) gave up a one-out single to John Rohner (2 for 3) and then got Michael McLeer to hit a potential double-play grounder to second baseman Jack Poole. The ball was misplayed, with no outs recorded.

No. 8 hitter Christian Schaffer promptly singled to load the bases. Hobbs got Jeremiah Chessie to ground to third for a force at home but Chessie, hustling out of the box, beat the throw to first to keep the inning alive.

Cody Bowker, down 0-2 in the count, worked a walk off Hobbs after staying off a 1-2 pitch ruled just outside to force in the first run.

Henry Lausier, who entered the game batting under .200, drove in two with a single. After Brady Graffam was hit by a pitch to reload the bases, Frink followed with another two-run single. The sixth run scored on an infield single by Brayden Williams.

“One through nine we really have a good order,” said Thornton assistant coach Tim Smith, filling in for head coach Jason Lariviere who was sick. “And take nothing away from Kopetski. He has a great arm and he’s the one who kept us in it.”

Given a 6-2 lead, Kopetski worked around seven baserunners over the next four scoreless innings, helped in the third inning by a nice running catch in left by Lausier with two-on and no outs.

“I felt like I needed to throw more off-speed. They were getting around on the fastball in the first inning, hitting it where it was pitched,” Kopetski said.

Thornton had just one hit after the second, a single by Schaffer against Heffernan, who pitched three scoreless innings of relief.

South Portland scored two unearned runs in the sixth as Thornton Academy made three errors and Poole stroked an RBI single.

Frink, making his second pitching appearance in relief this season – and first in a pressure situation – got the save for Thornton, striking out two in the seventh inning.