The Azzurri thumped France 3-1 at the Parc des Princes via goals from Inter Milan pair Fede Dimarco and Davide Frattesi, along with Napoli's Giacomo Raspadori.
“Effectively, I saw an intensity during training that we didn’t have the other time (at the Euros),” Spalletti said.
“Perhaps the physical shape had a role. The season has just started, and there is new enthusiasm. The other time, it was the end (of the season), and there had been things that, perhaps, had led somebody to switch off earlier. We were slower.
“Then, there is a tactical situation, too. Having put players back in their positions, they bounced back tonight. Regardless of how this game went, we would have continued playing forever.
“It’s in the DNA of this group I’ve chosen for the Nations League and the World Cup qualifiers. Three, four or five players have stayed home this time, but generally we are convinced that this group can give us so much.”