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."
Marc Guehi believes Argentina have more to lose when they meet England in Wednesday's World Cup semi-final in Atlanta, insisting the reigning champions are expected to win.
Kylian Mbappe admits France were unable to execute their gameplan against Spain in the World Cup semi-finals, as they were eliminated after a 2-0 defeat in Dallas.
Didier Deschamps' tenure as France coach is set to conclude with Saturday's FIFA World Cup third-place play-off in Miami after they lost to Spain in the semi-finals.
Spain reached their first FIFA World Cup final in 16 years after putting on a football masterclass to convincingly beat France 2-0 at the Dallas Stadium.
