De la Fuente's selection decisions paid off as Fabian Ruiz, handed a starting role ahead of Pedri, gave Spain the lead before Merino came off the bench late in the game to score the winner.

Merino was introduced in the 86th minute and needed just two minutes to make the difference. The midfielder reacted quickest after Belgium substitute goalkeeper Senne Lammens failed to hold Pau Cubarsi's low effort, firing Spain into the last four.

It was the third time Merino has scored a winning goal as a substitute in a knockout match under De la Fuente. He also netted the extra-time winner against Germany in the Euro 2024 quarter-finals and struck late against Portugal in the last 16 of this World Cup.

"It's unfair that Mikel doesn't play from the start, but it would also be unfair if someone else were left out," De la Fuente said.

"Only 11 can play, and they understand that. They know the role they have to play at any given moment. When they go onto the pitch, they know exactly what they have to do. That's why it's a pleasure to be their manager."

The Spain coach insisted his team's success is built on the strength of the entire squad rather than the starting line-up.

"What matters is the team," he said. "It doesn't matter who starts the match. Everyone is important, even those who haven't played."

De la Fuente also praised the attitude of his players, saying their professionalism has helped create a united dressing room despite the fierce competition for places.

"One of our strengths is that we have not only the best players in the world, but also the best people," he said.

"They make it easy for everyone to work together. We have built everything on respect, and this national team is an example of that."

Spain now face tournament favourites France in Tuesday's semi-final at Dallas Stadium, with a place in the World Cup final at stake.

"France have already shown extraordinary quality, and so have we," De la Fuente said. "The match is wide open. It will require fresh, energetic players, but now that we're here, we're going to give it our all."

Borussia Dortmund score late winner at Mainz in Bundesliga action