The Italian side advanced to the knockout stage thanks to goals from Brayan Perea and Felipe Anderson, and will progress as group winners should they beat Trabzonspor in their final fixture.
"There are many positives from this away win, starting from qualification and the possibility of finishing top in the group," Petkovic told Sky Sport Italia.
"Considering what has been happening to us recently, the team showed character and joy in its football. I liked the way the team played, as the youngsters are supported by the more experienced players.
"It's a shame that it only ended 2-0, as we could've had a bigger scoreline."
The Biancocelesti are currently eighth in Serie A with just one win in their last five games.