Atletico won the first-leg 4-0, with all four goals coming before halftime on Thursday night.
Afterwards Garcia, who was sent off late on, told reporters in the mixed zone: "They outplayed us in the first half in every way: intensity, desire, attitude...
"The second half was exactly what we should have done from the start. The good thing is that there are still 90 minutes left and we are more than capable of equalizing and advancing. I am one hundred percent convinced.
"It's no excuse for them not being more motivated. They completely outplayed us in the first half. Now there's a game left at home."
On the second-leg, Garcia also said: "There are 90 minutes left at home, with our fans, with the team we have and the players we've recovered. I have no doubt we can turn it around."