The world champions could easily have been behind at half-time after a poor first 45 minutes in which China captain Zheng Zhi passed up two great opportunities.
However, the introduction of Andres Iniesta after the interval made a huge difference as wave upon wave of Spanish attack was finally rewarded six minutes from time when the Barcelona midfielder squared for David Silva to slot home the winner.
Del Bosque told the Spanish Football Federation's website: "We were a little lazy in the first half and they were also more of a unit and withdrawn in terms of their positioning. They made us uncomfortable and created danger.
"In the second half we put more people forward and had more security and speed in our play and created more chances. We dominated the game in the second period and played almost the entire time in their half.
"We are a week away from the start of the championships and we go with a good taste in our mouth after this game."
Silva was one of just five Spanish players to play the full 90 minutes and could well have sealed his place in the starting line-up for the reigning champions' opening game of the Euros against Italy on Saturday with a fine performance full of invention.
However the Manchester City midfielder was keen to highlight the contribution of Iniesta.
He said: "Iniesta is an incredible player, he handed me the goal and the truth is when you play with him, everything is easier.
"In the first half we were a little slow but in the end we created a lot of chances and had the luck to get the goal and win the game.
"We hope to be at 100% for the Italy game because we know for sure that they will be.
"We are desperate to make history by becoming the first side to win three major championships back to back but we know that it will be very difficult because every team has the capability to make it hard for us."