City had been second best before the break as they trailed to an early Marquinhos header, though Guardiola felt they were architects of their own issues due to a lack of experience.
However, a spectacular turnaround means City have a slender lead to take into the return fixture at the Etihad Stadium, where even a 1-0 loss will be enough to secure the club a first final appearance in the competition.
"Sometimes you need to be more relaxed, a little bit more yourself," Guardiola told BT Sport.
"In the first half, it was normal. There are 180 minutes and you don't want to lose the ball, you don't play free.
"We changed a little bit the way we press, we were more aggressive as the first 20 minutes we were so passive.
"The last 10-15 minutes of the first half, then into the second half, we were more aggressive - and it is not easy to be that way with [Kylian] Mbappe, Neymar and [Angel] Di Maria, but we found the goals and could have scored another one.
"In general, I'm so satisfied for the performance. But this is halfway. We still have many more minutes to beat them, and PSG is a team where anything can happen."
City have now won their past 18 away matches in all competitions, scoring 46 goals during the run while conceding just nine.
PSG have won in Manchester once already this season – they triumphed 3-1 against City's neighbors United in the group stages in December – but will be without Idrissa Gueye for the second leg.
The midfielder became the first player to be sent off twice in a single Champions League campaign since Real Madrid's Alvaro Arbeloa in 2012-13 following a late tackle on Ilkay Gundogan.
Guardiola made clear that while City have control at the halfway stage, they must remain true to their methods as they aim to remain on course for a famous treble.
"At 1-0 they were good, we couldn't press well and didn't have good possession in the right positions," the Spaniard – twice a Champions League winner while in charge of Barcelona – said.
"Sometimes that is normal. This club doesn't have much experience in this competition in the last stages, especially semi-finals, but I think this is going to help us realise that we have to be ourselves, or anything can happen.
"In the second half we were incredibly aggressive and played really well.
"All I want is for us to be ourselves in the second leg. If we are good it is playing in a certain way, we cannot do it differently."