The World Cup holders needed a second-half brace from all-time leading scorer David Villa to seal the win in their final warm-up game in Washington.
Spain dictated play throughout the contest but were far from their free-flowing best against El Salvador, having been kept goalless to half-time, while they squandered a number of opportunities, including a Cesc Fabregas penalty at FedEx Field.
"Juanfran played the entire 90 minutes and held up, Diego Costa played for 70 and he could've gone more but we decided to take him out," he told reporters post-game.
"With these 23 players, we're going to Brazil.
"We lacked continuity and accuracy in the final third, but we dictated the match.
"We feel good and we're optimistic about the start of the competition. We didn't have many chances on goal but they were good and defended very well.
"But I'm not bothered by the way they played because if we take the initiative, I'm sure that in the majority of the games, we'll have room to pass."
"We know what David Villa can do, in confined spaces, he's one of the best strikers in the world," Del Bosque said.
