Chelsea right-back Cesar Azpilicueta, 23, Malaga playmaker Isco, 20, and Atletico Madrid midfielder Mario Suarez, 25, all stepped up in Doha and showed the slow transition to a new generation of players was progressing smoothly.
"They are players who will improve our squad and who have adapted normally to the group without any problems," Spain coach Del Bosque told a news conference.
"They did what they had to do. They were faithful to the characteristics that prompted us to call them up."
Casillas will not be back after surgery on a finger in time for Spain's World Cup qualifier at home to Finland on March 22, or for the trip to play France four days later.
Barcelona's Victor Valdes was a reliable substitute in goal, however, and is likely to be in the number one jersey when Spain take on the Group I joint-leaders in a clash of huge significance in Paris next month.
"It's two-and-a-half months since we were all together to play a game," added the avuncular Del Bosque, who always places a high premium on dressing room harmony.
"We have six weeks until we play Finland. It was important for us to get together ahead of these games. The most important aspect of it is the contact between the players.
"We should remember what awaits us in March. We start from now preparing for two extremely difficult encounters. If the spirit between us all is healthy and positive we will be closer to succeeding."
"We have had routines established for a long time now, and we have a fairly stable squad," former Real Madrid boss Del Bosque added.
"The important thing is to incorporate new players and not to lose the competitive spirit, whether we are playing a friendly or not. We have to know how to compete. Time with the national team is important, and the players know that."
