Spain have been one of the most impressive teams in the Euros, beating 2018 World Cup finalists Croatia and European champions Italy – plus Albania – in the group stage and Georgia in the last 16.
Their young wingers Lamine Yamal, who is just 16, and Nico Williams, 21, have been two of the stars of the tournament.
But they had to win this one in a different way, with the pair – and striker Alvaro Morata – all replaced at 1-0.
De la Fuente said: “I’m proud to coach players like this, players that are insatiable.
“They’re used to competing at the highest level and they have an opportunity to win the tournament.
“How far we will get, we will see, but we’re absolutely convinced that we can get very far with this side.
“We are so happy, but our euphoria is totally under control. We know tomorrow is already another day.”
Spain will be without suspended defenders Dani Carvajal and Robin le Normand for the semi-final – and midfielder Pedri is an injury doubt after going off in the eighth minute for Olmo.
Fifteen players were shown cards in the game – the second highest in a European Championship game – with seven for Spain, including Le Normand and Carvajal, who was sent off for two bookings.
“I played in the 80s – if you want to watch a video of the 80s and see how football was played back then, you know I don’t get scared. I have a friend who says, ‘what do you want, to get kissed?” De la Fuente said.
“This is football, I am not afraid of these things – the game is played to the limit, I am not complaining about the toughness of the opposing team, I rather appreciate what we as a team have done.”
Olmo, who plays in Germany for RB Leipzig and was named man of the match, said: “The heart is always more important than the legs.
“Let’s take it easy and calmly, because in four days we have the semi-finals. We are going to enjoy, celebrate, but calmly and calmly, because in a few days we have the semi-finals.”
Former Scotland winger Pat Nevin, watching for BBC Radio 5 Live, said: “You talk about tactics and systems but it became much more human than that.
“It was about who was going to be least exhausted and who would switch off for that split second. And it turned out to be the Germans.
“Well done to Spain. They are not just a pretty team, they have grit as well. But they also have a lot of suspensions so will find it hard to get past whoever they play in the semi-final.”