A stunning first-half display, in which returning captain Marquinhos scored the opener, was followed by a meek performance following the break as Kevin De Bruyne and Riyad Mahrez scored, perhaps fortunately, to complete a deserved turnaround.
“I must say in the second half PSG were protective and not progressive any more,” Wenger told beIN SPORTS. “Is it because they were not physically capable?
“After 1-1, they collapsed completely. They become emotional and aggressive in a stupid way.”
Wenger said PSG’s patchy domestic form – the French champions lie in second spot, one point behind leaders Lille with four games to play – had affected their confidence.
“What was interesting is that you could see that when it was 1-1, PSG mentally collapsed,” Wenger added. “This is the consequence of the team losing eight games in the league. This has an impact.
“When it’s 1-1 the team knows they have lost many games, they carry that. It’s not like the season before when they were unbeatable in the league.
“You could see the confidence dropped considerably and the mental impact when Man City equalised, for the semi-final of a Champions League, was too big.”
Additional reporting by Reuters.