A lethargic scoreless draw with Cape Verde led to doubts over Spain's ability to go all the way at the tournament, but a 4-0 victory, inspired by the return of Lamine Yamal to the starting lineup, has restored the faith.
"I think it's crazy to question this team," the manager said.
"We have been unbeaten for 33 consecutive games. You can have better days, worse days, normal days, but questioning, doubting this generation of very young footballers with a bright future, I think it's unfair."
De la Fuente said on Saturday that his players had been motivated by the critics, and he reiterated that point after the win.
"Nobody enjoys receiving criticism," he said.
"Their pride was hurt, of course, because this is not a reality. We can do even better than this, as we've shown on other occasions.
"Those remarks that they hear, of course, sometimes make them react. And that's good because it's a very committed, dedicated team with amazing quality.
"You are great professionals. But there are things I wouldn't like to listen to. And that's why I don't listen to any programme, for example, and that's why I try to stay positive and to isolate myself from all that noise."
Much was made of Mikel Oyarzabal's unhappy record of failing to touch the ball in the opening half hour against Cape Verde, but the Spanish striker provided an assist and scored twice in the first half against Saudi Arabia.
Oyarzabal became the second player to have three goal involvements in the opening 25 minutes of a World Cup game since records began in 1966, after Hungary's Laszlo Fazekas against El Salvador in 1982.
"People who know about football value him greatly," De la Fuente said.
"Unfortunately, there are people who think that he doesn't have such a big impact. The impact Mikel has on the team is massive, probably bigger than any other player could have in the world.
"I'm convinced that he's a footballer that can really make history in Spanish football. His numbers are crazy. So I just celebrate his performance and hopefully we will be able to value him properly."
Spain have four points in Group H, and Saudi Arabia are on one after two games each. Cape Verde and Uruguay, both with one point, meet later on Sunday. Spain's final group game is against Uruguay on Friday.
Click here for more on Spain's win over Saudi Arabia
FIFA World Cup 2026
The 2026 World Cup is taking place from June 11th to July 19th in the United States, Canada and Mexico. The tournament features 48 national teams and is played at 16 modern stadiums.
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