Conestoga struck first when senior Blake Hamblett drilled the ball into the back corner of the cage off a penalty corner.
Hamblett, who has committed to Dartmouth for lacrosse, went on to record two assists for the Pioneers and was instrumental in Conestoga's fourth goal, which sealed the game late.
"It wasn't even just my effort, it was a whole team effort," Hamblett said. "We knew how much this game meant."
Eight minutes later, the Pioneers struck again. Oliver Everts took a weak shot and the ball trickled across the goal line untouched.
And with three minutes remaining in the half, with Conestoga capitalizing on every opportunity, Hamblett got through traffic at the top of the circle and found Karla Di Pietro, who knocked in the goal.
It appeared that the Pioneers would not give Downingtown West any mercy. But the disciplined Whippets bounced back in the second half, earning corner after corner and controlling the game. With 15 minutes to play, Nikki Freeman crossed the ball to the left post where Meghan Vermeil was waiting for the tip-in.
The Whippets never gave up, but a series of yellow cards that kept captain Molly McGuckin out for much of the remainder of the game dismantled hopes of a comeback.
Conestoga also fell prey to yellow cards as well, though, as Hamblett was pulled for five minutes after not giving Downingtown West the regulated five yards for a free hit. Hamblett's yellow card put the teams at even strength until she returned with just under three minutes to play.
"We did the best thing we could - we just didn't let it into our heads," Hamblett said. "It obviously didn't help, but I don't think we let it get to us."
The Pioneers will take on top-seeded Spring-Ford on Wednesday at 3:30.
Conestoga 3 1 - 4
Downingtown West 0 1 - 1
Goals: C- Blake Hamblett, Oliver Everts (2), Karla DiPietro. DW- Meghan Vermeil. Saves: C- Chloe Johnson 8, DW- Colleen Brade 7.