After Xabi Alonso's penalty, the Dutch bounced back with a diving header from Robin van Persie in the 44th minute and goals in the second half by Arjen Robben (twice), Stefan de Vrij and another by Van Persie, reports Xinhua.
"I never thought it would end in a 5-1 win," Van Gaal said after the match. "After Spain's penalty I was thinking of changing tactics at half-time, but at that moment Van Persie scored his wonderful header, with so much class. A really beautiful goal."
"Spain played one-on-one defense on Van Persie and Robben," Van Gaal added. "They could just not stop them. I always told that we could beat them because they want to dominate. I did expect us to score the way we did. I think the people have enjoyed it."
Man of the Match Robin van Persie praised his coach for preparing the team well and explaining how to exploit Spain's weaknesses with the new 5-3-2 system.
"It's incredible, because it was exactly as Van Gaal and the staff predicted for us," Van Persie said. "For us, a dream came true and we have to enjoy it. Everyone in Holland must go out and celebrate."
"I am so proud of these guys," Robben said. "For many of us it was the first match at a major tournament, especially in defense. They did a great job. I did not worry after the first goal by Spain. We knew that they wanted to dominate. We just had to be patient."
Holland will now play Australia June 18 in Porto Alegre, while Spain meet Chile, who beat Australia 3-1 Friday, in Rio de Janeiro. A win against Australia would practically send the Dutch to the second round.
"This is a nice start, but we have nothing yet," Van Gaal said. "If we do not win our next game against Australia we have made no progress, but now we are obviously in a good position."