Courtois was preferred to Petr Cech for Tuesday's first leg at the Parc des Princes and the Belgium goalkeeper produced some fine saves to deny PSG victory.
Branislav Ivanovic's first-half header gave the Premier League leaders a scarcely deserved lead, but Edinson Cavani headed his 17th goal of the season to equalise nine minutes after the break.
The Ligue 1 champions looked the more likely to force a victory, but Chelsea held on for a draw at a stadium where they were beaten 3-1 in the quarter-finals last season before winning 2-0 at home to progress on away goals.
Mourinho praised Courtois' performance and the Chelsea manager was happy to return to London on level terms with an away goal ahead of the second leg at Stamford Bridge on March 11.
He told ITV: "We could have lost, so I think the result is a positive one.
"I don't say very good because it depends on the result of the second leg but it is a positive result against a very good team with fantastic technical players. It was a difficult match.
"When you see the performance of our goalkeeper you have to say yes, he made two or three important saves in the game."
PSG were depleted by injuries for the clash in the French capital, but Mourinho revealed his side's preparations had also not been ideal ahead of the game.
He added: "Sometimes people speak about the players when they are injured and do not play. There are injured players who play, they don't train to play. I had five players in this game who did not train since Everton. So we felt that a little.
"I am happy with the result because two legs is now one leg with everything to be decided at Stamford Bridge."
