The South Americans remain their continent's only hope of winning the trophy, after hosts Brazil capitulated in their semi-final with Germany, losing 7-1.
Despite packing an in-form Lionel Messi in his side, Sabella insisted his men have already achieved their aims in Brazil and any win from here on is a bonus.
"As football is illogical, I don't know what will happen. I do know that to reach the final we have to improve," Sabella said on Tuesday.
"We came here to go as far as possible. The objective was to reach the quarter-finals after 24 years, but now we want to reach the final.
"There mustn't be frustration or sadness if we don't get there. Whatever the semi-final result, we have already won."
Dutch winger Arjen Robben is Argentina's biggest threat for the clash at Arena Corinthians in Sao Paulo, according to Sabella.
"Robben is a player who can certainly go one-on-one and that way create superiority, so we'll keep an eye on him for special treatment," he said.
"We need to surround him, stop him from getting up a head of steam, otherwise it'll be very difficult to get the ball back."
Sabella said Di Maria's replacement - Enzo Perez - was below the Real Madrid man's level, but the Benfica midfielder would still play his role.
"I have always said Di Maria is a very important player, as he brings balance, won the [UEFA] Champions League, is wanted all over Europe and gets on very well with Messi," Sabella said.
"Perez has fewer moments of magic but he holds the space well, is suited to major competitions and has matured a great deal in psychological terms. It's no coincidence he was named best player in Portugal."
"Sergio Aguero is improving and trained a little today. We'll see how the game develops and whether he'll be needed," the coach said.
