"It's just a reaction. When a ball's coming right at you, you want to defend yourself and play it," said Selinsgrove coach Cathy Keiser. "That was tough. It really opened up space back there."
Shortly after the infraction, Weinstock slipped the ball from Klingler near midfield and made her decisive charge.
Seminary (15-5-1) advances to play District 1 champion Upper Perkiomen, a winner over Donegal, in Saturday's quarterfinals.
Selinsgrove celebrated its 50th season by reclaiming the Heartland-I title it surrendered last year for the first time since 1998 and by winning its ninth consecutive District 4 crown. The Seals finished 20-2.
"They wanted to come out and prove themselves, and I think they did that," Keiser said after a 14-game win streak ended. "They're a special group, very caring of each other. We had some awesome leaders this year and I think that's what we're all going to miss."
The Seals controlled the first half if they didn't build a 3-1 lead on the Knights as they had Oct. 4 in Selinsgrove.
Brooke Zeiders' tackle on Weinstock and pass to Lexi Horst produced the corner that led to the game's first goal. Klingler handled Zeiders' insert and sent a pass to the far post that Zeiders punched in.
Seminary's pressure generated its first corner a little more than 6 minutes into the second half, and more quickly followed.
Alexis Quick's inserts to Morgan Malone on the left side developed too slowly to attack openings. However, after a string of three fruitless corners, Malone sent a long hit straight-on from near the 25 that Gabby Grossman tipped past Seals keeper Courtney McCartney. The junior had a bead on Malone's ball, but couldn't stop the tip when she flailed her left leg.
Selinsgrove had just one shot and two corners over the game's final 36:36.