The Spain coach has used all three of his goalkeepers - Casillas, Pepe Reina and Victor Valdes - during the tournament, selecting a different one in each of the group games.
But he hinted that Casillas will be his first choice for the remaining games of the competition.
In an interview with AS, Del Bosque said: "The statistics are there for everyone to see - Casillas has played over 140 games for us. All the goalkeepers are stupendous, but Casillas is the one who is the number one.
"You want to know who's more likely to play: it's Casillas. But they are all great goalkeepers and any of them could play."
Spain have played with just one holding midfielder in the tournament, Sergio Busquets, unlike in the World Cup, Euro 2012 and in the majority of qualifying games, where Del Bosque deployed Xabi Alonso - who has missed the Confederations Cup through injury - alongside the Barcelona midfielder.
Another change has been to play with a natural centre-forward, either Roberto Soldado or Fernando Torres, compared with last year's European Championship, when Cesc Fabregas played in the 'false nine' role in Spain's two games with Italy.
Del Bosque played down the significance of the change, explaining: "We haven't changed too much, the names have changed and you have to adapt to them. The system of play is just a drawing and then the players develop it. We have had to adapt to losing Xabi Alonso.
"Against Italy we made our plans in order to deal with (Andrea) Pirlo, who dictated the play and who would play deeper, so it was in our interest for Cesc to track him.
"We might not use the same tactics again, because it's possible that Pirlo won't play (due to injury)."
It had been suggested that Del Bosque switched to playing one holding midfielder to appease Xavi Hernandez.
Del Bosque denied it, while admitting that the Barcelona midfielder was not entirely happy with the former system during Euro 2012.
"Xavi felt a little uneasy at that time and we had a conversation, but it never got serious," Del Bosque added.
"He is our leader on the pitch, the one who manages the team from inside and who dictates the play."
The coach also declared he had a cohesive way of working with the team and was in constant dialogue with the players.
He said: "I speak with the players every day, how could I not? It isn't a symptom of weakness, it is a sign of strength that a coach, the one who is in charge, speaks with the players."
Del Bosque also laughed off the report from a Brazilian newspaper that the team had held an alcohol-fuelled party after the game with Uruguay, adding: "When we went to play in Argentina after the World Cup it was reported that I was dancing on top of a table until the early hours of the morning. I have never danced in my life. This is the same type of thing."