Spain's ghosts of recent World Cup horror shows reappeared in Atlanta as the European champions were held 0-0 by debutants Cape Verde in their opening game on Monday.
Lamine Yamal was left on the bench as the Barcelona superstar is eased back to fitness after nearly two months out with a hamstring injury and even his appearance as a second-half substitute failed to break down Cape Verde's dogged defence.
Since winning the World Cup for the first time in 2010, Spain have not won a knockout game and their inability to make dominance of possession count was reminiscent of their meek exits in 2018 and 2022.
"Reality has to sink in," said Spain boss Luis de la Fuente. "This is a World Cup. We know that some teams, on paper, they are not better than us and we thought that we were far better than them. But then it's a struggle to win."
Blessed with what coach De la Fuente claimed is the best squad in the competition, Spain were considered among the pre-tournament favourites to go all the way and lift the World Cup on July 19.
But the importance of Yamal and Nico Williams to their chances of success was underlined by a flat performance.
Williams also had an injury-disrupted season at Athletic Bilbao and was not introduced until the 87th minute.
Ranked 67 in the world, Cape Verde were making their debut on the global stage and did a nation of just over 500,000 people proud.
In stark contrast to the searing temperatures faced by some other sides, Atlanta's state-of-the-art air conditioned stadium meant there was no excuses for the slow tempo of Spain's build-up.
Indeed the mid-half hydration break was met by boos with fans frustrated at the break in play despite the cool conditions.
It took until six minutes before half-time for Spain to seriously threaten.
Marc Cucurella, fresh for sealing his move from Chelsea to Real Madrid, sent over a teasing cross that Ferran Torres turned onto the crossbar and Cape Verde goalkeeper Vozinha got back on his feet to turn Mikel Oyarzabal's looping header over the bar.
Torres tested Vozinha again moments later before Aymeric Laporte's header from a corner was also clawed away by the Cape Verde number one just before half-time.
The break came at a good time for the Blue Sharks and they comfortably held out in the second period until Yamal's entrance after the second hydration break.
Billed as one of the stars of the tournament, the 18-year-old's appearance instantly lifted the crowd and injected life into the pedestrian Spanish attack.
His first involvement set up a decent opening for fellow substitute Mikel Merino which was too close to Vozinha.
Yamal also began the move that saw Oyarzabal's effort deflected over with Spain's best chance of the second half.
Cape Verde nearly snatched a famous victory in the final minute of the 90 when Dani Borges planted a header too close to Unai Simon.
But even without a winner, 40-year-old Vozinha was reduced to tears at full-time as Cape Verde produced the biggest shock of the tournament so far.
"I've worked all my life for this, for this moment, for this dream," said Vozinha, who plays for Chaves in the Portuguese second division.
"A lot of generations in the past dreamed of this, they didn't achieve it," he added. "The dream came true, for all of us."
Spain's road to victory in 2010 also began disappointingly with defeat to Switzerland, but they have much to work on ahead of facing Saudi Arabia in Atlanta once more on Sunday.
Cape Verde next take on Uruguay in Miami.
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