Barca must overcome a 2-0 deficit to progress.
"The best way to lift ourselves is to think about what we've got left. We have to think positively. Things aren't going the way we want them to, and there are things we have to improve. But the only way to improve is by working hard and having a positive, winning mentality," said Mascherano.
"We have to take a step forward the positive thing is that it's in our hands and football is always better when you're not depending on other results going your way."