Crescenta Valley (2-1) will meet Sherman Oaks Notre Dame in the tournament's third-place game at 6 p.m. today. West Ranch (3-0) will battle Pasadena in the title contest at 7:30.
"We didn't play well and I don't think we were quite ready [for West Ranch] after a couple of easy wins," Crescenta Valley Coach Jason Perez said. "We made some mental mistakes and it comes down to experience.
"We didn't rebound very well and poor rebounding and poor execution will cost you. We also had some communication breakdowns on defense."
Crescenta Valley, which opened the tournament with victories against Immaculate Heart and Simi Valley, took a 53-52 lead on a three-pointer by Yoon with 90 seconds left in the contest. However, West Ranch's Michele Arima answered on the ensuing possession with a basket with 1:07 remaining.
Clinging to a one-point lead with 16 seconds left, the Wildcats were called for a five-second violation. Crescenta Valley had one last opportunity, but an errant pass landed out of bounds with 5.9 seconds remaining.
"Every time we got the lead, we then had a breakdown," Perez said. "They answered on their next possession whenever we took the lead."
West Ranch held a 27-21 halftime lead, but then Yoon, a forward, gained some momentum with her clutch outside shooting. Yoon scored the Falcons' first 10 points in the third quarter, including two from three-point territory. Yoon finished with 13 third-quarter points.
"I don't shoot threes that much," Yoon said. "I made the first one and that gave me confidence and I could trust myself."
The Falcons got 13 points from forward Ella Stepanian and six assists from guard Melanie Minas.
The Wildcats got 19 points from Arima and 14 rebounds from Hannah Green.