The Serie A outfit reached the last 16 in the UEFA Europa League with the victory after playing out a 0-0 draw in the first leg in Wales.
Late strikes from Gonzalo Higuain and Gokhan Inler proved decisive for Benitez's men as they set up a meeting with Porto.
Benitez believes Monk, the interim player-manager at the Premier League side after Michael Laudrup's sacking, has a bright future ahead of him.
"We are talking about a team which has played for a while in the system with the same ideas and the same style," the Spaniard said.
"So I told my players before that, and they knew the way they wanted to play and when a team plays without too much pressure you can play at your level.
"When you are under pressure you make too many mistakes, when you have too much pressure you can play at this level.
"I think that's credit to him, as I said before the first game I think he has a great future ahead of him."
Lorenzo Insigne had given Napoli a 17th-minute lead, but it was cancelled out by Jonathan de Guzman on the half-hour mark.
But two goals in the final 13 minutes proved to be the difference and Benitez said it was extremely tough for his side.
"Today wasn't an easy match. We were playing a very quick team. There was a lot of intensity from them, pressing, they were very fast in counter-attacks," Benitez said.
"What we tried to do as soon as we scored the second goal was to maintain possession of the ball and take our chances when they came."
