Saint Francis improved to 19-2 overall and 8-1 in the Crossroads League and now shares the league lead with Indiana Wesleyan.
The Wildcats had their 27-game regular-season win streak halted and 20-game 2012-13 win streak stopped , as well.
The Cougars had dropped four straight in the series.
The Wildcats (20-1, 8-1 CL) tied the game at 29 early in the second half when Taylor Goshert buried a 3-pointer at 17:24, but it was the only time the Cougars shared the lead.
After trading turnovers, Jenelle Wilson launched a 3-pointer from the corner that whistled through the twine for a 32-29
Saint Francis led at the 16:05 mark and started a 16-2 run that put it into a comfortable 45-31 lead with 11:32 to play after Ridley's jumper.
Wilson hit all three of USF’s 3-point shots and finished with 11 points, while Meghan Slusher added 10.
“They’ve got a great team, but we were able to execute our game plan and take away some things they like to do,” Saint Francis coach Gary Andrews said in a release. “Brooke did a great job defending against (Paige) Smith and Skylarr just had a great game on both ends of the court. That run was huge after they had rallied to tie the game.
"When they cut it to five, I thought we did an excellent job of maintaining our composure," Andrews added. "We took care of the ball and still worked to get the best shot possible, then knocked them in. We had to keep scoring, keep attacking when the opportunity was there. Great job."
Saint Francis led by 14 one more time at 47-33 on a Ridley second-chance score with 10:52 to play in the second half. Indiana Wesleyan rallied cutting the deficit to five three times between 5:03 and 1:51.
Katrina Blackmon powered in a second-chance bucket trimming the Cougar advantage to 54-49 with 1:51 to play. Shurn had the answer with a drive to the basket for two and a 56-49 lead at 1:41.
The Wildcats got no closer than six once in the time remaining, while Saint Francis connected on 6-of-6 shots from the free throw line to complete the upset.
Shurn scored 12 points in the first half and came back with 13 in the second half.
"We don't take any team lightly," Shurn said. "I thought a key was limiting touches for (Paige Smith) in the second half. I was a little nervous when we got the big lead, because we’ve had a tendency to let teams back in it. I thought we did a decent job of keeping our poise, getting shots and finishing free throws. We talked about how to attack their zone during a timeout and we just had to be patient. We were and got Meghan some shots. I just was aggressive on offense."
Saint Francis was perfect at the free-throw stripe hitting 15-of-15 shots. Indiana Wesleyan hit 14-of-20 free throw attempts.
Shurn was 9-for-9 at the line to help her surpass her previous career best of 23 points. She scored five points in the Saint Francis run that put the Cougars in front by 14.
"We did a good job of making stops and getting the ball out in transition and converting some opportunities during that stretch," Andrews said.
"First of all, this has never felt so good to beat a team like this," Slusher said. "This is my fourth season and we've never been a good enough team to actually contend with them and we did a (heckuva) job in my eyes."
Drake, who didn't play in the three losses to the Wildcats in 2011-12, only scored two points (she averages 15.2 ppg), but she took care of the point and dished out three assists.
"We had to stick to our game plan," Drake said. "That's what I did. I just tried to come ready."
And then there was Ridley, who has set a Saint Francis single-season record for blocked shots with 60 including four against Indiana Wesleyan.
"Brooke really had to battle in there and shut them down in an area they are pretty strong at," Slusher said.
"She was phenomenal in there," Drake added.
“It feels great to finally beat them,” Ridley said after the game. She was in the fifth or sixth grade the last time USF knocked off IWU as the No. 1 team. “I was really excited to play them and happy to contribute to our win tonight.”
Claire Ray led the Wildcats in scoring with 16 points, while Paige Smith added 14 and Katrina Blackmon 10 for IWU.
Saint Francis is now 6-0 at home and starts the second-half schedule 'gauntlet' on Saturday when 24th-ranked Huntington travels to Saint Francis for the rematch at 1 p.m.
"We got off to a good start,” Andrews said. “That was important because we gained some confidence learning we could compete against No. 1.”