The European champions have begun to show the form expected of them in recent Euro 2016 qualifying matches, however they have now not won a friendly match since June.
Goals from Stefan De Vrij and Davy Klaassen inside 16 minutes secured victory for Guus Hiddink's side, while goalkeeper Kenneth Vermeer was on hand to deny Spain on the rare occasions they tested the Dutch goal.
"The first 20 minutes have burdened us," said Del Bosque. "It seems impossible we wouldn't score.
"We have taken command of the game, we've been all over them and have reached the penalty area, but we lacked a goal."
The 64-year-old handed first appearances to Juanmi and Vitolo after their impressive club form, and Del Bosque was pleased with what he saw.
"The two rookies have had good performances," he added. "Vitolo has been very active and Juanmi looked like scoring."
