The first leg clash between the two Ligue 1 clubs saw Folarin Balogun score twice for the hosts in the opening 18 minutes before Vitinha had his penalty saved to compound matters.
But after Desire Doue came on for injured Ousmane Dembele, the match turned and defending champions PSG went on to secure a one-goal advantage for the return leg.
"Normally, when a team starts a match like that, the most likely outcome is a loss,” Luis Enrique said.
“It was catastrophic. It's impossible to start a match like that. The first two times they overcame our pressure and entered our half, they scored. They made some very good plays.
“After that, it's difficult to have confidence, but we showed our mental strength. Plus, we missed a penalty, so it was a chance to regain confidence. In the last six times we've played here, this is only the second time we've won, which shows how difficult it is.”
The 20-year-old Doue scored twice and provided a third for Achraf Hakimi, just days after he had turned in a poor performance against Stade Rennais last Friday and was dropped for the Monaco clash.
“I'm happy for him because this past week, everyone criticised and tore Doue apart, but he was sensational, he showed his character. He helped the team at the best possible time.”
Dembele’s injury would be assessed, the coach added. “He took a knock in the first 15 minutes, then he couldn't run.”
The return leg at the Parc des Princes will be next Wednesday. “Considering how the match started, I'm happy with the result. But the match in Paris will be difficult, it will be a different story,” Luis Enrique warned.