Luis Enrique warned overconfidence could cause Spain's downfall when they face Germany in their second Group E clash on Sunday.
Spain dominated their opening contest, trouncing Costa Rica 7-0 with the highest margin of any win in Qatar so far and netting the most goals the country have ever scored in a World Cup match.
It was a performance that surprised even their manager, who urged his players to remain measured in their response to the decisive victory.
Luis Enrique said: "We tried to manage that victory with all normality. We got the three points, that's it.
"It was a resounding victory that fills us with confidence, but we shouldn't have too much confidence. We are facing an opponent, Germany, against which we cannot be overconfident otherwise they will hammer us.
"We have a very smart squad, smart enough to know that we have to respect our opponent, and we will have to give it our all. It's a great challenge."
The former Real Madrid and Barcelona midfielder originally took over his national team in 2018, then stepped down for personal reasons while his young daughter underwent cancer treatment.
He was reappointed in 2019, following her death at the age of nine, and made his World Cup managerial debut in the Costa Rica clash on Wednesday, one he admitted went beyond his wildest expectations.
Luis Enrique said: "Well, in your debut you expect to go as far as possible. I did not expect to see such a good version of my team playing so well, it was such a pleasure to see my team performing the way they did."
Germany, who surprisingly lost their opening match against Japan, will be tougher opposition for Spain but Luis Enrique is looking forward to the test.
He said: "You might find it interesting, but I do so much better when I'm managing problems, and that's stupid. Don't laugh.
"I feel more at ease when I'm in the face of adversity, when I have to lift the mood of my players, to bring everything you've got inside, to make the most of my roots, my origins.
"As a coach I have very successful moments, but when I perform at my best is when I'm in the face of adversity and hardship."