Cahill, who arrived at Stamford Bridge from Bolton Wanderers in the winter, admits that the experience he has taken from facing the world champions in the major European competition will prove vital.
"I need experience in this competition," he said.
"It was great to get that. The experience I have taken from this will be vital going forward.
"If we can replicate the result [in Barcelona], that would be fantastic. It would be unbelievable."
Cahill and company kept a clean sheet against Barcelona in the first leg of their semi-final clash.