The Italians gained some retribution for their 4-0 Euro 2012 final loss to Spain with a 2-0 round-of-16 win over the two-time defending champions on Monday.
Giorgio Chiellini and Graziano Pelle scored for Italy as their supreme defensive organisation kept Spain at bay.
Antonio Conte's men had been rated - by both national and global media - as perhaps the worst Italian team at a major international tournament in recent memory, something Buffon says the coach and the rest of the squad had not forgotten.
"There is a long and tortuous road ahead of us and very difficult teams on our path. We cannot yet say that it is a great Euros for Italy, as we’re only in the quarter-finals," he told Sky Sport Italia after the game.
"Having said that, I will not forget that many thought very little of us before the tournament began. We have proved that we were vastly underrated and I am proud of that."
On the win itself, Buffon was proud to see his team end a horror run of results against Spain.
"We put in a good performance, but after the first half the 1-0 result was frankly less than we deserved," he said.
"We knew that the game could change after the break. That proved to be the case, but we didn't just focus on defending. In fact, we had several chances to double our lead before Pelle's goal.
"After many years of defeats to Spain, we made up for it. OK, it was only a round-of-16 tie, but it's better than nothing."