Manchester United pair Phil Jones and Danny Welbeck and Everton's Jack Rodwell all drew praise from Capello, while Tottenham Hotspur right-back Kyle Walker also came on late to win his first cap.
Jones, who plays in the back four for United but earned his second England cap in midfield, was given the unenviable task of breaking up the visitors' mesmerising passing patterns, and despite chasing shadows at times he stuck to his task.
Rodwell came on as a second-half subtitute for his first appearance for the senior team and worried Spain's back four with his energy when linking up with fellow substitute Welbeck despite most of the play taking place at the other end.
"The victory was important for the players' confidence and for the confidence of the fans," Capello told reporters after England's first defeat of reigning world champions since 1980.
"But the most important thing for me was the performance of Rodwell, of Welbeck and Jones.
"These are really good young players and I saw that these players will be very important for the next years. They played without fear, with personality and techncially and physically showed they are ready to play with the seniors."
Capello said Welbeck, who has three caps, and Walker will start against Sweden in another friendly at Wembley on Tuesday.
Captain John Terry will also return, the Italian coach confirmed, despite the furore over his alleged racist comment to Queens Park Rangers defender Anton Ferdinand in last month's West London derby at Loftus Road.
Terry did no more than warm up on the touchline on Saturday, but the solid performances of Joleon Lescott and Phil Jagielka showed England are well stocked in central defence as thoughts turn to next year's European Championship.
"The two centre-backs played fantastic, really good," Capello said. "Every time Spain tried to pass through they were in good positions. They played with big confidence - and it's impossible if you don't defend with confidence against Spain."
