Ronaldo's second squirmed through the arms of De Gea, with the Manchester United stopper adding to the error that he made in the pre-tournament friendly against Switzerland.
Nacho, however, has insisted that De Gea "seems fine" as he looks to overcome the disappointment.
"He seems fine to me. He knows what happened but, as players, we are always exposed to these things. When mishaps happen, we unite and we're all with him 100%," Nacho told reporters.
"He is a world-class goalkeeper and we are lucky to have a player of his calibre. He has no doubts about his own ability and he will bring a lot to the team in the future."
Spain's next Group B clash is against Iran - who beat Morocco 1-0 in their opener - on Wednesday night.