Milan came from behind at San Siro on Thursday (AEST) and sits seventh in Serie A, boosting its chances of European qualification.
After Jasmin Kurtic gave Parma the lead, goals from Franck Kessie, Alessio Romagnoli and Hakan Calhanoglu saw Milan to victory.
Ibrahimovic played 90 minutes and Pioli said the 38-year-old's determination was pushing Milan.
"He demands the maximum from himself and from others," the Milan coach told Sky Sport Italia.
"He knows that the team is growing and he is giving his best, then he becomes a lion on the field. He gets very angry, sometimes out of turn, but we know how he is made.
"His anger is positive … it is a determination that has made us and is making us grow.
"The mental strength of the team has increased, we are more aware of our quality."
Milan had found themselves behind before Kessie produced a moment of magic, the 23-year-old's 30-yard rocket bringing his side level.
Kessie is up to four league goals this season and Pioli said he was happy with the midfielder.
"He and I had some relationship difficulties, then we understood each other better," he said.
"I think it is essential to get the most out of players. He is proving to be a very high level player."
Milan is in action again on Sunday (AEST), when it hosts Bologna.