The Blues have a mountain to climb if they are to overcome the Ligue 1 champions tomorrow night, having lost 3-1 in last week's quarter-final first leg at the Parc des Princes.
Mourinho acknowledged that his side will go into the match as underdogs to progress, but insists that they believe in their ability to overturn the deficit.
"Reasons to believe? I think the reasons are not important. I believe and my players believe. That's the most important thing. I think if Paris tomorrow is knocked out it will be a big disappointment for them. If tomorrow we are knocked out it's something that, in this moment, lots of people are expecting," Mourinho told reporters.
"We have to enjoy the risk of the situation. At 9.30 we can be out and we know that we have this risk. But at 7.45 we have chances to be in the semi-final. We have to be at 7.45 with a smile on our faces, go in, play, give everything. At 9.30, let's see what happens. But at 7.45 we believe that we can do it.
"I think we are going to win, really. In the end of the two legs, I think we are going to score more goals than them. In this moment it's 3-1, I think in the end it can be 4-3 or 5-4. If I don't think that way I don't go tomorrow. And I go and I'm happy to go."
Only two teams in Champions League history have come back from two goals down in a second leg, with Chelsea being on the receiving end in 2000 and launching their own comeback in the last 16 against Napoli in 2012.