The reigning European champions ultimately cruised into the last eight thanks to goals from Sergio Ramos and Alvaro Morata either side of a Dries Mertens own goal, which was initially credited to the Spain centre-back.
Mertens had put Napoli 1-0 up in a first half which was dominated by the hosts in Italy, and it was put to Zidane that they were lucky to progress in relatively comfortable circumstances in the end.
"I don't think we were lucky," the Frenchman told Mediaset Premium. "Good luck doesn't exist in football.
"The 3-1 result speaks clearly; the difference was made by our quality, even if we suffered at times.
"In the first half we suffered. We didn't get into the game properly, while Napoli did.
"They took the initiative at first, but we emerged in the long run. We cannot play well every time.
"We have to focus on the good things and that we had a much better second half."