Portugal head coach Carlos Queiroz admitted Spain were deserved winners in their last 16 clash on Tuesday.
David Villa scored the decisive goal for the European champions as they set up a quarter-final meeting with Paraguay.
Portugal spurned chances in the first half to break the deadlock before Spain were rewarded for their growing dominance.
"It was an extremely difficult game but Spain moved the ball very well and had more possession and any team that does that can control the game better," said Queiroz.
"Spain won with merit. But I would also like to underscore the fact that Portugal played with a great degree of dignity and ambition and I believe the fans have justifiable reason to be proud of the way the team has played.
"Spain were much more effective moving the ball around. We were looking for chances on the counter-attack. We had our chances - we just didn't score.
"We showed ambition and desire to win but it just wasn't possible. We'll have to come back stronger."
Queiroz also highlighted the display of goalkeeper Eduardo, who made a number of fine saves to frustrate Spain.
"His performance was brilliant," Queiroz said. "He saved and kept the team fighting for the result."
The shot-stopper himself added: "To lose by one goal in a championship hurts very badly."