Liverpool had the benefit of playing the second leg at Anfield on those occasions and it was to prove decisive in both games.
The opposite applies this time around as Chelsea play the second leg at home on April 30 and Barnes feels the Liverpool players will have to mentally prepare themselves for the crowd being against them at Stamford Bridge.
Barnes said: "Liverpool have the psychological edge as they have knocked them out twice.
"But on the last two occasions it has been the other way around which has helped Liverpool.
"The decisive leg is always the second leg so while the Anfield factor is important in inspiring the team and getting a result, I feel being at home in the second leg can be important in helping you to go through.
"No matter what happens in the first leg, they are not going to reach the Final on the outcome of that result.
"There are four great teams with equal ability. Manchester United have shown over the whole season they are the most consistent team and are better than Liverpool and Chelsea.
"But on a one-off consistency goes out the window and all four teams are capable of winning it."