PSG were leading 2-1 in Wednesday's first-leg quarter-final encounter at Parc des Princes as Ezequiel Lavezzi's early strike and an own goal from David Luiz sandwiched Eden Hazard's penalty.
There was then late drama when attacking midfielder Pastore waltzed his way through the Chelsea defence before squeezing his drive past Petr Cech.
Jose Mourinho's Chelsea side face a difficult task in overturning the deficit at Stamford Bridge on Tuesday, but Pastore has warned that the job is not complete.
Speaking to PSG's official website, he said: "It's an excellent result to win 3-1 against Chelsea in a really good match of football.
"I am very happy to have scored that third goal, because it will be an important goal in the return leg.
"Chelsea are a great team with great players so we will have to stay focused there, because it is still a Champions League quarter-final."
That sentiment was echoed by team-mate Thiago Motta, with the midfielder expecting Chelsea to apply plenty of pressure on their own turf.
"It's an excellent result," he commented.
"We have played a huge match of football. In the first half, it was very difficult for us, and then in the second, we made life very difficult for them.
"We have to play a very tricky return leg at Stamford Bridge now and resist the pressure from Chelsea to qualify for the semi-finals."
