The Blaugrana narrowly progressed past a strong Atletico Madrid side in the semi final, edging their opponents out on away goals following a heated second-leg affair at Camp Nou.
The return fixture against Atleti yielded plenty of action, most notably the third of three red cards being dubiously handed to Luis Suarez after a mild brush with Koke.
And with the Uruguayan set to watch from the stands, Cillessen has faith that under-fire striker Alcacer can rise to the occasion.
“It's terrible for them,” the keeper said, reserving sympathy for Sergi Roberto, who also saw red.
“As a team we have to win it for them. [Suarez] wasn't happy. He's a great striker and it's nice to have him in the team.
“[But] Paco scored in our last match and that was very important for us, so now it's his turn to step up and I think he's going to do it.”
Cillessen himself was a rare stand-out performer for the Catalans as he produced a string of saves to keep Antoine Griezmann and Co. at bay, leading to reporters asking whether it was his best performance in a Barca shirt.
“I think so,” he said, “ but I preferred the game against Gladbach where I had nothing to do. When I don't have anything to do it's much better!”