The 4-1 win sets up a Euros quarteerfinal against hosts Germany.
De la Fuente said afterwards: "The match is eight or nine out of ten. The goal made us doubt, but we quickly regained control. We are ambitious and we knew that no one has won the first four matches of a Euro.
"We have the best team and the best players. We are going to fight for it and we know what we have ahead of us, which is Germany. There is quality, commitment and confidence. The next opponent is a powerhouse, with great players. It is the well-known German machine. It will be a very close match, but we are very confident of our game."
He continued, "The moments of doubt came because of the result, not because of the game. We were patient and they knew how to overcome them. It's a good lesson for us. We had to chip away and wear down our opponents.
"Football has that, bad moments and the rivals can also get ahead. We were not anxious or hasty. We only had moments of doubt after the goal. These situations make us a little better.
"A match lasts a lot of minutes and there are alternatives and the players must know that. Now the eight best in Europe are there and what determines whether you are a strong team is knowing how to row and push at the right moment. The difficulty increases with each match and now Germany awaits."
On Lamine Yamal, De la Fuente added: "He played a good game, but I think he's going to play better. Maybe he should have taken more time off at certain moments. He should have stopped a bit more and not tried again and again. Today's game will serve as a learning experience for him because of the situations he'll encounter in future games."