The Blues boss defended his decision to start with Andre Schurrle and suggests that he expected more from Fernando Torres when he introduced him as a second-half substitute
Mourinho's side was level at halftime in the first leg, with Eden Hazard's penalty having secured a crucial away goal after Ezequiel Lavezzi had struck to give the hosts the lead at Parc des Princes.
But the visitors paid for some slack defending in the second half, with first David Luiz scoring an own goal before Javier Pastore ghosted in from the touchline to sneak home a third at Petr Cech's near post.
Mourinho struggled to put into words his frustration at his side's lapse in concentration, telling Sky Sports: "It's ridiculous [the defending for the third PSG goal].
"We played against a great team full of good players, especially their attacking players are fantastic. You would expect them to score fantastic goals. You don't expect them to score the goals they scored.
"The first goal was a ball in an easy position. After the cross comes in we assist the striker and nobody fought the second ball in a crucial position.
"The second goal it was one of my players on his own goal line but that's obviously unlucky.
"But the way the team was positioned defensively was not the correct one. The third goal was even more sloppy; ridiculous."
The Chelsea boss concedes his side will now have a mountain to climb to reach the semifinals but is adamant that the tie is not yet over. He added: "It's a difficult job [to reach the semifinals] but not impossible.
"They are the kind of team that with the players they have that out of nothing they can score goals. So we don't have an easy job. We are not a team full of talent to score lots of goals especially at this level but we never know. We have to try. We have to go with everything.
"I changed at 1-1 because I thought that Fernando [Torres] could give us more depth than Andre [Schurrle]. The team was comfortable with Andre, had good control of the game, good ball possession, Andre was working back. I thought Fernando could give us a bit more."