The score finished 1-1 in the first leg after Diego Ribas' stunning opener for Atletico was ruled out by Neymar’s equalizer.
Following a difficult tie at Camp Nou last week - and with all four clashes between the teams having been draws this season - Iniesta knows his teammates will have to be at their best to eliminate Diego Simeone's men on Wednesday.
"It would be nice to play a great game and reach the semifinals, which is where we want to be," the attacker told Mundo Deportivo. "It was an intense game, both physically and mentally, and there was a lot of pressure [from Atletico in the first leg].
"We will fight for it knowing it will be very intense from the first minute to the last. We have played Atletico four times this season and drawn against them on all four occasions. The conclusion is we are evenly matched. Atletico require you to be very focused and not slip up."
The 29-year-old is set to make his 500th appearance for the Catalans on Wednesday and says it will be a moment of pride for him to earn the landmark cap.
"It is something very special, which makes me very happy," he said. "The years pass and you keep competing and feeling good. This is the hardest club to play for."