First, Duncan Preston broke through the Brunswick defense for a stirring goal.

Then, his South Portland boys’ lacrosse team broke through for its first Class A championship Saturday, earning a 10-8 win in a fast-paced game at Fitzpatrick Stadium.

Preston, a midfielder, scored four goals to lead the Red Riots. But the one that symbolized the team’s spirit came early in the second quarter, after Preston scooped up a loose ball near his goal as a yellow flag flew into the air. Defenders collapsed on him, hacking at his stick, shoving and jostling him. But he was undeterred, racing all the way to the Brunswick goal to unleash a shot that put his team ahead 4-1.

“I saw they hit (goalie) T-Moe (Hellier) in the head,” Preston said of the infraction that drew the flag. “I knew if I dropped the ball, the play would be over, so I just thought to myself, ‘No one’s going to take the ball from my stick.’ I went through, got past my guy, no one slid to me, walked right up to the goal.”

It was one of three first-half goals for Preston, all on rugged plays welcomed by a senior who was a quarterback in football. It staked the Red Riots to a 6-2 halftime lead.

Brunswick (13-3) scored five goals in a third-quarter blitz that twice saw the Dragons cut the deficit to one. Cam Glover and Tyler Sullivan, both juniors, finished with three goals apiece.

“We’ve got a lot of fight in us,” Glover said. “We came out a little nervous, but once we got the faceoffs going, the ground balls, we got into our flow. They just had it in them, they played a hell of a game.”

Jack Fiorini scored two first-half goals and Andrew Whipple added a pair in the second half to help South Portland make history. Hellier made nine of his 12 saves in the first half.

“When they came out and scored those four goals in the second half, it was a little concerning, but I had faith in our team,” Hellier said of the opening five minutes of the third quarter.

“Last year, we might have lost that lead. We were a lot younger. But this year we’ve been battle-tested and we can win those close games, so we don’t get rattled.”

South Portland (14-1) was cruising through its season before losing to Scarborough in the final game of the regular season. The Red Riots won the Western Maine title with a stunning last-minute comeback against Thornton Academy.

Now, after seven years of steady growth, the program has reached the top step.

“This program has been climbing and climbing and climbing,” Coach Tom Fiorini said. “We’re now here, and I’d like to think it’s just going to help us keep growing.”