The Blues have been given little hope of prolonging their European campaign into the spring, despite the last-16 clash being delicately poised at 1-1 after the opening 90 minutes in West London.
Cahill was a member of the Chelsea side that knocked Barca out of the competition en route to lifting the trophy six years ago, however, and believes that he and his teammates have the necessary spirit to pull off another big win in Catalonia.
"Chelsea are being written off but it is the nature of the beast," the London Evening Standard quotes him as saying. "If you're looking at facts, this club has been very, very successful over the last 10 years, and since I have been here over the past six years.
"You can have ups and downs. I can speak about myself and when I have been down I have bounced back. The same goes for the club. Let's go there with confidence we can put in a good show and do the best we possibly can to get through to the next round.
"It's poised nicely. We've got one game to try to go through against world-class opposition. We know it's going to be tough but we're ready for the challenge."
Barcelona are unbeaten in La Liga this season and have not tasted defeat at Camp Nou in any competition since August.