Highlights - Paraguay 0-1 Spain
Coach Vicente Del Bosque admitted that Spain struggled to find their usual rhythm after sneaking past Paraguay to reach a first World Cup semi-final.
Spain needed a late winner from David Villa to win 1-0 and book a Wednesday clash against Germany, who earlier on Saturday thrashed Argentina 4-0.
"We weren't as at ease in possession as in other games and it's important to be comfortable," said the 59-year-old.
Del Bosque also conceded that Germany are "the best team at the moment."
Spain were pushed right to the brink by a committed Paraguay side who could have taken the lead had Iker Casillas not saved Oscar Cordoba's 59th-minute penalty.
It feels good but nothing is done yet
Del Bosque's side missed their own chance from the spot just minutes later when Xabi Alonso had his second attempt saved, although they continued to probe Paraguay and Villa - who is now the tournament's top scorer with five goals - eventually came to the rescue.
"We're in the last four in the world," said Del Bosque. "It's a good moment for Spanish football.
"We didn't play well mainly because we didn't get enough of the ball."
Spain deservedly beat Germany to take the 2008 European Championship title, but Joachim Loew's side are now being hailed as the most impressive team in South Africa - a point not lost on Del Bosque's players as they still try to find their best collective form.
"Quite apart from their results, the Germans are playing brilliantly, so they must be tremendously motivated," said Spain and Barcelona midfielder Andres Iniesta.
"It will be a game between two rivals who enjoy having the ball and I think it will be a beautiful battle."
Arsenal captain Cesc Fabregas, who came on as a second-half substitute for the still-struggling Liverpool striker Fernando Torres, was keen to stress that Spain are yet to peak despite making history.
"It feels good but nothing is done yet," he told the BBC. "The semi-final is nothing if we don't reach the final. We are happy, it was a difficult game but we want to improve and get into the final."
Fabregas, who will now seek a doctor's advice after falling badly on his shoulder, added: "We watched the [Germany] game this afternoon, they played really well.
"We know it will be a difficult game, they are one of the best teams here. We have to be positive and do our best to beat them."