Napoli scored twice in the first half as they upstaged Milan 2-1 in Saturday's enthralling fixture at San Siro.
Two goals in nine minutes from Lorenzo Insigne and Jose Callejon inspired third-placed Napoli in Milan, with Juraj Kucka's 37th-minute goal not enough to derail Sarri and Co.
"We showed our usual limitations, but there were steps forward, because we held out for the win and started to control the ball a bit better as time wore on," Sarri told Mediaset Premium.
"These lads have got to realise they have great potential, without losing their humility, and find that determination to become a great team.
"We're already a good team, but can become great.
"I did see a step forward in terms of mentality today and we showed maturity, so that's an excellent sign."