Western's two third-period goals came from the blue-line as Anthea Lasis and Brianna Iazzolino scored at 5:59 and 13:09, respectively, to send the Mustangs into the semifinals.
"Take a look at our stats, after Kendra Broad our next two leading scorers are Katelyn Gosling and Brianna Iazzolino — and Anthea Lasis is going to be a stud in this league," said Western head coach Chris Higgins. "I've been saying that all season. She's got a heavy shot from the point and she's going to get a lot of goals in this league."
The opening period was primarily a back-and-forth affair before Western's Stacey Scott opened the scoring with a power-play goal from the slot with just over three minutes remaining in the frame.
Although Western controlled possession in the opening minutes of the second, Moncton got a power-play goal from Amelie Dion midway through the period. Following a blocked shot from the point, Dion picked up the bouncing puck and slid it along the ice to tie the game at 1-1.
Moncton was in prime position to take the lead thanks to three consecutive penalties from Western late in the second and early in the third, but the Mustangs were able to hold the Aigles Bleues power play at bay.
Shortly after killing off their latest penalty Western took the lead off a booming slap shot from Lasis that sailed into the top corner of the net. Iazzolino added the insurance goal a little over seven minutes later.
"I give a lot of credit to Moncton, they did their homework on the video, on the power play they took away our high option, we didn't adjust quick enough to it," said Higgins. "They got in the way of our defencemen, our pucks weren't getting through, they're a well-coached team."
Kelly Campbell stopped 27-of-28 shots for Western while Gabrielle Forget made 21 saves for Moncton.
The Mustangs will face the Montreal Carabins, who beat the Alberta Pandas 4-3 in Saturday's other quarter-final.
Despite being down 3-2 with less than 10 minutes to play in the third period, Montreal made the comeback— with the tying goal and the winning goal coming less than one minute apart.
"I'm very proud, especially of the way we came back from behind," said Carabins head coach Isabelle Leclaire. "Very honestly this didn't happen much this season. This is where maybe we struggled a bit when we were behind in the game. It has been a tougher this year in that aspect so I'm very happy that we came back.
"I knew (the Pandas) were a very good defensive team, I knew they were intense in every aspect of the game and that they had a great goalie and that's what they showed tonight."
Marion Allemoz broke a 3-3 deadlock at 12:09 of the third period for the Carabins, who also got goals from Laurie Mercier, Lore Baudrit and Ariane Barker.
Lindsey Cunningham, Jessie Olfert, and Natasha Steblin supplied the offence for the Pandas.
Montreal's Elodie Rousseau-Sirois made 22 saves while Lindsey Post turned away 16-of-20 shots for Alberta.
St.FX and McGill will meet in the other semifinal after quarter-final victories on Thursday.