Spain fell to their first home defeat under Del Bosque as Toni Kroos' 89th-minute strike gave the world champions victory in Vigo.
The result marked Spain's third loss in six games since their group-stage exit at the World Cup.
Del Bosque was understandably disappointed with the result, but the 63-year-old is more focused on building a side to challenge for future honours.
"We are in a period of transition and we want to continue looking to the future with optimism, but we are not entirely happy with the outcome," Del Bosque said.
Although Del Bosque admits the deposed world champions are rebuilding, he was pleased with the overall performance of his side.
He added: "I agree with the assessment that it was an even, balanced game, and we showed that we could out-play them, but we must praise Kroos' goal."
Spain resume competitive action in a Euro 2016 qualifier with Ukraine in March.
