The French manager looked on as Angel Di Maria struck twice in the opening half against his former club before Thomas Meunier concluded a counter-attack in the dying moments of the game. The scoreline didn't flatter PSG as the visiting Spaniards were punished for an insipid Champions League display.
"Clearly they were better than us in every department - in the way they played, in midfield," Zidane said after the group-stage defeat, as quoted by Reuters.
"What upset me is that we did not put enough intensity in the game and at that level of competition, it's not possible," he added.
Eden Hazard was handed his full debut as a Real Madrid player, but there was an otherwise familiar appearance to Zidane's attack. Karim Benzema was joined by Gareth Bale and James Rodriguez - both of whom had uncertain futures over the summer - in the starting lineup but, despite boasting such an impressive arsenal, Los Blancos failed to hit the target with any of their 10 attempts on goal.
"Failing to create proper chances with the players we have up front - Gareth Bale, Karim Benzema, and Eden Hazard - is a weird feeling," Zidane said.
"You can play badly but if you have the intensity, if you fight for the ball, you're in the game," he added.
Real Madrid follow the midweek continental setback with a trip to high-flying Sevilla during Sunday's La Liga slate.