The winning play had echoes of another overtime against Radnor, two years ago. Foust took the opening draw control of overtime and sprinted straight down the field and scored to give Harriton a 14-13 win.
Saturday, she did the same, but her first shot missed the goal. Given a second possession, she didn't miss, cranking the game-winner from the middle of the field.
The early control and strike was especially critical as Harriton entered the overtime a player down.
"As soon as I got the draw, I just knew," Foust said. "I really needed to get the ball back and dodge anyone I needed to get to the goal."
After scoring first, Harriton didn't reach the goal much early on. Radnor (20-5) stormed to a 5-1 lead with 4 minutes, 1 second left in the first half.
It was an eyebrow-raising score, considering Harriton had won the previous two meetings, including a 13-6 win late last month.
Harriton (25-2) scored the next six goals, including two from Jane Henderson, to take a 7-5 lead.
"It was just all nerves," Foust said. "We all knew we could beat this team."
Radnor's Shannon Quinn scored her second goal to break the tide, and Kate Stanley tied it on a free-position strike.
Then it was the goalies' turn to take center stage for the final 13:31.
Radnor's Grace Collins stopped Jane Henderson on a free-position try, and Melina Avery returned the favor on a shot from Shannon Quinn that also caught the pipe.
Avery made eight saves.
"She's not much of a talker, she's kind of silent back there," Foust said. "But we can always count on her, no matter what the situation is."
The win capped a title run that seemed improbable when Dick took over six seasons ago. As Radnor won the first two PIAA titles in 2009 and 2010, Harriton was going through growing pains, including a couple of thumpings at the hands of the Red Raiders.
Even Foust, who will go on to play field hockey at the University of Virginia, didn't see this coming in those salad days.
"No way," she said, shaking her head.
Radnor 5 2 0 - 7
Harriton 3 4 1 - 8
R: Shannon Quinn 2, Sydney Cowles 1, Reilly Masterson 1, Sara Curley 1, Brooke Pancoast 1, Kate Stanley 1.
H: Caleigh Foust 5, Maura Henderson 1, Jane Henderson 2.
Saves: R-Grace Collins 9; H-Melina Avery 8.
Contact Tim McManus at email@example.com. Follow @ByTimMcManus on Twitter.