The Wolverines will face Woodford County, a 9-2 winner over Mercer County, for the regional title on Thursday night after avenging a 3-1 loss at Boyle on Sept. 11.
Western Hills took the fight to Boyle right from the beginning, holding the Rebels without a shot for the first 16 minutes.
"I don't think we were prepared as well as we could've been, and that's my fault," Deem said. "I told the girls we win together and we lose together, but I'll take full responsibility when we lose."
Deem said the blame does not lie with Boyle goalkeeper Tiffany Webb, who saw all four of Western Hills' shootout tries pass to her left and into the net.
"They were nice shots, really well placed," Deem said. "There's nothing she can do about that."
Meanwhile, Western Hills goalkeeper Tiffany Cammuse made up for a mistake that led to Boyle's only regulation goal.
Cammuse blocked Sarah Hall's shot at the start of the shootout to give her team an advantage. Shots by Lydia Hignite and Marianna Richardson got by, but Cammuse stopped a shot by Webb to preserve Western Hills' 3-2 edge, and Rachel Mann put in the clinching kick for the Wolverines.
"Their keeper does a real good job of extending her body," Deem said.
Cammuse most impressive save may have come early in the third overtime period when she stopped a shot by Boyle's Joanna Frauenhoffer.
"I thought Joanna had won it," Deem said. "She hit a perfect shot, but their goalkeeper made an outstanding save. What can you do?"
Cammuse had helped Boyle take a 1-0 lead with 23:16 left in regulation when she tried to clear the ball but instead saw her kick carom off Boyle's Hall and back into the net.
Western Hills matched that goal when Alicia McCarty, who missed the teams' first meeting with an injury, put in the rebound after a missed shot by Beth Fox, tying the game with 28:15 to play.
After being outshot 7-5 in the first half, Boyle held a 12-6 edge in second-half shots.
"We responded well and had opportunities to finish; we just couldn't put the ball away," Deem said.
The Rebels dominated play in overtime, outshooting Western Hills 9-2 in two 10-minute periods and 6-0 in two five-minute sudden-death periods, and Deem said he felt the winning goal could come at any time.
"I was just waiting for it," he said. "I really felt like we had them on their heels. I felt in the overtime they didn't have any offense against us."
Deem said he was disappointed for the Boyle seniors, who led the Rebels to consecutive 28th District titles in their last two years.
"These four seniors, in their own way, have taken this program to a different level," he said.
They won't be able to forget their final game, and Deem said he hopes Boyle's younger players will remember it just as vividly.
"I asked them to remember this feeling," Deem said, "so they don't ever have to relive it."