The Blues travel to Spain on Tuesday looking to defend a 1-0 lead that they gained at Stamford Bridge last Wednesday.
Despite the advantage, Brazilian international Ramires believes that Barca should still be considered the stronger bet to progress.
"The pressure will be on Barcelona. They have to score and we can exploit that," Ramires told the Sun on Sunday. "They don't intimidate me. Barca are not invincible.
"We have showed it at Stamford Bridge. We have taken the first step - but our advantage is minimal. They are favourites."
The winners of the tie will face either Real Madrid or Bayern Munich in next month's final.