SCARBOROUGH — It took just one goal for Thornton Academy to effectively end Scarborough’s four-year reign as Class A boys’ lacrosse champion.

When Thornton’s Isaac Sinclair put his team on the scoreboard 5 minutes, 33 seconds into Saturday’s Western Class A semifinal, excitement on the visiting sideline was obvious. The Trojans scored three more goals to close out the first quarter. They added three more to start the second.

The Trojans drained the drama from the game early and then kept up the onslaught in a 13-4 victory that was five years in the making.

That’s how long Ryan Hersey has been coaching Thornton Academy, which lost all nine previous encounters with the Red Storm. In each of those, Scarborough scored first.

That didn’t happen Saturday.

“Coach made a point in saying we need to get the first goal today, get them worried, and that worked,” said Trojan senior attack Cody Falton, who finished with four goals and four assists. “As soon as we got that first goal, it just kind of snowballed and we got hot and put up big goals in a hurry.”

Third-seeded Thornton Academy (11-3) sprinted to a 7-0 lead and then parked a trio of big defensemen in front of goalie Jack Grondin. Scarborough (10-4) could never solve that zone, or get Grondin out of the zone that he was in. The senior made 19 saves.

“They were getting to them before they could get their arms out and really place a shot,” Hersey said of defenders Tyler LaPointe, Dan Giroux and Chase Conklin. Giroux and Conklin started as freshmen three years ago when Scarborough beat Thornton in the regional final. “They had to hurry things, which made their shots just go off by six inches, and that’s all you need in this game.”

And when the shots were on target, Grondin was always in position to swat them away.

Hersey said the coaches got his attention in practice this week by suggesting that backup Chris Camire was outplaying him. Grondin had all the motivation he needed.

“They have a lot of good shooters and mix it up well. You’ve just got to be ready for anything,” Grondin said.

“The defense, they made them take tough shots, and the score shows.”

Sinclair finished with four goals and two assists, and Zach Bryant added three goals as the Trojans were able to push the pace throughout the game. Even with a big lead, they didn’t deviate from that attack.

For the second-seeded Red Storm, it was a humbling way to be dethroned. But Coach Joe Hezlep praised his players for their run of four straight state titles.

“I don’t feel like we played any worse today than we have any other time; we just weren’t able to finish,” Hezlep said. “I’m going to tell them very clearly that I’m as proud of them as any team over the past four years.”

It was obvious how much the game meant to Thornton just by listening to the players shouting themselves hoarse, encouraging teammates and counting down the minutes until they could finally say they had beaten Scarborough.

It was arguably the biggest win in program history, and sets up a regional final Wednesday at top-ranked South Portland, which beat Gorham 16-3

“That is the best 48 minutes that I’ve seen Thornton Academy play in the five years that I’ve been coach,” Hersey said. “This should prove to them that we can play with anybody.”