Napoli won thanks to goals from David Neres, Romelu Lukaku (pen) and Scott McTominay.
Stellini said afterwards: "It's right to call it very important, for various reasons. The first is that we were on a difficult pitch against a strong team with a very large roster.
"And then the second is that we had some shortcomings and wanting to demonstrate the importance of our work and how much the boys follow us, it is even more important. We are happy, we thank the entire work group that gave solidity to the team despite the absences.
"We bring with us great energy from the victory, the boys must be proud of what they have done since the beginning of the year. We are happy because even those who have played less have played a great game. Today we feel this maturity but we will have to demonstrate it from game to game.
"We were aware that we had to rebuild something important and the credit goes to the boys, from day one they have shown great availability, with the desire to return to the usual levels of Napoli. Let's not make comparisons with past seasons: we are leading the team in a good job, which fills us with pride. Today's match shows that the boys are following us."