Just last week, it was South River, not Old Mill, doing the celebrating after the Seahawks beat the Patriots in the final game of the regular season and clinched a postseason berth. Friday night, it was Old Mill’s turn.

Seven days after dropping its regular season finale against the Seahawks, second-seeded Old Mill beat third-seeded South River, 21-7, in the first round of the Maryland 4A East region playoffs at home Friday night, clinching a berth in the region final next week.

The Patriots earned the victory on the back of a strong rushing attack, led by running back Shawn Brown’s season-high 225 yards and two touchdowns, along with a stingy defense that held South River’s potent offense to its second-lowest point total of the season.

“In practice, we just looked at a lot of film on them, just kept looking at our opponent that we were lining up against,” Brown said of the familiarity bred by playing South River back-to-back weeks. “It just helped us so good. Last week when we lost it took a lot out of us, so we had to just come out here and play so hard.”

Behind Brown, Patriots running back Raykwon Young had 154 total yards, 72 on the ground and 82 through the air, and a touchdown. Old Mill quarterback Brady Ludwig completed 4 of 7 passes for 91 yards and a touchdown.

Seahawks quarterback Connor Cox, who threw for just over 2,900 yards on the season entering Friday’s game and 222 yards last week against Old Mill last week, completed just 11 of 35 passes this week for a pedestrian 180 yards. Cox had 39 touchdown passes this season and four against the Patriots a week ago, but Old Mill harassed him in the backfield all night and picked him off twice.

Cox’s favorite target, wide receiver Eric Young, caught just three passes for 55 yards and was held out of the end zone for just the second time this season. South River’s leading rusher this season, Lavon Chaney, had just 17 yards on eight carries. As a team, South River mustered just 260 yards of offense.

“Connor Cox, he’s really good at running around. We got to him a couple times. Last week that didn’t happen. Just seeing him once gave us a little bit of a knowledge of what he was capable of,” Old Mill Coach Chad McCormick said. “Our guys just played at a different level than what they did last week. Our young men on offense and defense, they upped their level of football for this game and that results in the scoreboard and the victory.”

Arundel will play host next week to Meade, which upset top-seeded Arundel 36-28 in the region’s other game. Kickoff is scheduled for 7 p.m.