Spain won 1-0 thanks to Real Sociedad midfielder Martin Zubimendi's strike.
De la Fuente later said, "Martín is a sure value, he plays calmly and with great judgement. I don't know if we were better in the second half because of him or because of the team. He doesn't score much but he is starting to get going with us, we celebrate that. He is one of the best footballers in the world in his position.
"There was a lot of tension (at halftime) and you always want to transmit drive. Just like in Serbia, in the first half we lacked tact, handling the ball quicker and with more speed.
"Denmark is a good opponent, they made things difficult for us. The changes gave us more energy, the team felt more comfortable. The matches last 90 minutes but there can be alternations, especially against powerful rivals."
On captain Alvaro Morata, De la Fuente added: "Morata has been outstanding. He has missed the goal on two or three occasions when the goalkeeper has intervened. Álvaro gave us depth, support and had a great game. He is one of the best in the world in that position for what he offers us. If he continues like this he will score goals and continue helping the team. He is very complete and important for us."