Real Madrid shot-stopper Casillas acknowledged that Italy were unfortunate to lose.
“Penalties are a lottery and we were lucky to win,” Casillas said after the game.
“On Sunday we will play a great Brazil side. We will have to do well to win.”
Coach Vicente Del Bosque agreed with his captain.
“Italy are a very strong side who deserved to take the lead in the first half,” he said. “As the game went on we got better and deserved the victory in extra time.
“Over the course of the match things balanced out and Italy looked increasingly tired, which allowed us to come out.”
Spain will face Brazil in the final on Sunday.