The Huskies countered late in the first quarter on Josh Wilson's unassisted goal, but two unanswered goals by the Cavaliers, from Caleb Runci and Dylan McDermott, pushed the lead to 4-1 midway through quarter two.
Brandon Burris scored for Patterson Mill to cut the lead to 4-2 at the half.
Eight seconds into the second half, South Carroll's Brown added his second goal, the game's only goal in the third quarter, for a 5-2 lead.
Patterson Mill responded in the fourth quarter on back-to-back goals by Wilson, eight minutes apart, to close to within one, 5-4, with 3:32 to play. Another Wilson shot, which could have tied the game, 5-5, caromed innocently off the side pipe.
South Carroll's McDermott then scored a dagger at the 2:49 mark to end the scoring. McDermott ended the night with two goals and one assist and Willingham had a goal and two assists.
"From where we came from, the beginning of the season, to where we are now, I would say it's the shock of the tournament right now," South Carroll head coach Bill McDermott said. "I think people were expecting a all-Harford championship and we had other ideas."
Wilson led all scorers with three goals and Brendan Egan added two assists.
South Carroll goalie Taylor Schmitz finished with 12 saves and Patterson Mill keeper Jay Kuhn made eight saves.
Bel Air falls in two OTs
Thirty seconds into the second sudden-death overtime at Friday's 4A/3A boys lacrosse semifinal at Franklin, South River's Ben Chisolm tucked away a shot from 15 yards out to send the Bel Air Bobcats home with a season-ending loss, 10-9.
Bel Air's leading scorer was Parker Jones, who netted four goals, while teammate Tom Hollenback scored a hat trick in the loss. Carson Kalama netted two goals for the Bobcats.
The 4A/3A North champion Bel Air held a 9-8 advantage with just over six minutes left in regulation.
Bel Air led, 4-3, after one quarter of play, and went into the halftime break tied with South River, 5-5. At the end of the third quarter, Bel Air was up, 9-8.