Spain completely outclassed the pre-tournament favourites, producing a dominant display that was a far cry from their goalless group-stage draw against Cape Verde.
Mikel Oyarzabal put La Roja ahead from the penalty spot before Pedro Porro capped a slick team move with a second-half finish to wrap up the win, with Spain scoring once in each half.
The European Championship-winning coach said his players had timed their improvement perfectly for the latter stages of the competition as they prepare to face either England or Argentina in the final.
De la Fuente also sought to ease concerns over Lamine Yamal after the forward seemed to be struggling after the match, insisting there was no reason for alarm.
However, he confirmed goalscorer Porro had suffered a muscular injury, casting doubt over the defender's availability for the World Cup showpiece.
"We're so proud," he said. "This amazing generation of players has such a great attitude and is a role model for so many different values.
"We are united for a common cause. Now we have the last step, the toughest one. We'll have to improve and we'll try to do so.
"Of course we would have loved to win the first game but this is a process and it was all planned for us to reach these key moments in the best shape possible.
"Now we are in great shape, the players are very excited and we have reached a peak after this long season."
