Robin van Persie and Arjen Robben scored two goals apiece as Netherlands humiliated the defending champions 5-1.
Speaking after the match, Spanish coach refused to blame his goalkeeper Iker Casillas.
"I feel terrible but brave enough to take this defeat on the chin without getting depressed about it. I can't explain why we let in five goals," Del Bosque was quoted as saying on FIFA.com.
"We're not noted as being a defensive side, but we've always been resolute at the back. In the first half they pressurised us but we still managed to find some space. The game turned on a couple of long balls they played in behind us," he added.
"I feel terrible but brave enough to take this defeat on the chin."
According to the coach, the whole team underperformed in their Group B opening match.
"We can't blame Casillas. We lost because the whole team underperformed. Even though I'm not going to compare this defeat to the one we suffered to Switzerland four years ago, we have the experience and it's still just the three points that we've dropped. We need to look forward with the strength of an athlete who wants to overcome the next challenge," the coach explained.