De la Fuente got his tenure off to a promising start with a 3-0 home win against Norway on Saturday, though victory was only assured after to two late strikes from 33-year-old debutant Joselu, and the coach appeared lukewarm about the performance despite the scoreline.
De la Fuente, who took over Spain from Luis Enrique following the World Cup in Qatar, said he has warmed to the showing since.
"The feeling is always better after seeing it (on video) than on the field. I am very optimistic about what we are doing," De la Fuente told reporters in Glasgow on Monday.
"I am very critical on the field but more positive things came out of the game than bad things.
"I am now more optimistic because we have had time (together as a squad). We have detected many things to work on. Of course, we have to improve, but I saw a team committed, excited and hungry to win."
Scotland have not beaten Spain since 1984, but De la Fuente has seen recent progress in Tuesday’s opponents
and is taking nothing for granted.
"It's an important and difficult match against a powerful rival, with many (English) Premier League players. That speaks to the level of the squad," he said.
"There is no small rival these days. That is not a cliché and is especially true at international level. They will bring aggressiveness, intensity and quality.
"Scotland has evolved a lot (as a team), they are no longer so direct and aerial. They have good circulation (of the ball). We are prepared for it, for any scenario.
"The goal is to be first in the group, but it won't be easy."
