When Ba struck, the manager came racing out of his technical area towards his players to speak them as they celebrated by the corner flag.
And asked what had prompted his sprint, Mourinho said: "Not to celebrate - to tell Fernando (Torres, another substitute) and Demba the changes we had to do, because there was still three minutes plus added time and with that amount of time left, playing like we were playing, it was too risky.
"I wanted to use my two freshest players for a different job in the last period.
"We did enough in the beginning of the second half to score, but we couldn't and after that there was a bit of a contradiction in terms of what PSG are and what they were saying yesterday - they played pure counter-attack, with no ball possession, just getting behind using counter-attack and closing everything.
"It was difficult for us to penetrate in that second part of the second half, so I played Demba and Fernando. We had looked at different systems yesterday and the players knew what to do.
"Then Demba made a crucial finish for us and I think it was very much deserved.
"The team that decided to defend was punished. The team that gave everything, sometimes with their hearts, deserved to go through to the semis."
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