Routed in its opening match, Spain aims to avoid an unwanted World Cup hat-trick against Chile on Wednesday.
Another loss after its humbling 5-1 defeat by the Netherlands would almost certainly end Spain's title defense.
A group-stage elimination would make Spain the third straight European winner of the World Cup to flop in the group stage as defending champion.
"If we don't win we go home, and the consequences will be brutal," said Cesc Fabregas, a veteran of Spain's six-year run as the world's best national team.
Spain kicks off in mid-afternoon at Maracana Stadium, and should know what is at stake if it hopes to return there on July 13. Earlier Wednesday in Porto Alegre, the Dutch play an apparently over-matched Australia team already beaten 3-1 by Chile.
"After the terrible result against (the Netherlands) we know this is a final for us," midfielder Xabi Alonso said. "We expect a match filled with intensity."
Recent World Cup history suggests Spain could have seen this trouble coming.
In 2002, defending champion France exited without even scoring a goal in its group. In 2010, Italy's title defense also ended early and winless.
The key question for coach Vicente del Bosque is how much loyalty to show his proven title-winners — some of whom looked jaded against slick Dutch counter-attacking.
"It was a very hard defeat to swallow, but it is not a definitive loss," del Bosque said. "After the match we were very angry with ourselves, but we're shaking that off. We're professionals and we have to raise our game in the face of adversity."
Captain and goalkeeper Iker Casillas is in the line of fire, though his potential replacement was injured in training Sunday.
David De Gea of Manchester United strained a leg muscle and should be out for at least 10 days. Pepe Reina of Liverpool is del Bosque's other option.
Fabregas could return in the "False Nine" role of deep-lying striker which he excelled at in previous tournament triumphs.
"We have to win and we have to try and win by more than one goal, so we'll have to attack," said Fabregas, who could replace Diego Costa, his likely teammate at Chelsea next season.
Pedro Rodriguez could also start in place of David Silva, whose missed chance to put Spain 2-0 ahead last Friday was a turning point.
Those changes would still keep a core of 2010 veterans in place, while Atletico Madrid midfielder Koke represents a fresher look.
Among 13 Spain players who faced Chile in the group-stage in South Africa four years ago, 11 are in Brazil and still central to del Bosque's plans.
Spain won that match 2-1 in Pretoria, getting first-half goals from David Villa and Andres Iniesta.
Chile also has not changed much between World Cups, and nine who played Spain then are available Wednesday, including Arturo Vidal.
Vidal, the creative midfielder from Juventus, is still building fitness after knee surgery and managed one hour against Australia, leaving when Chile's 2-1 lead was most under threat.
If Vidal is below full strength, speedy forward Alexis Sanchez can compensate against several of his Barcelona teammates.
"I'm worried about the quality of Chile," del Bosque acknowledged.
AP Sports Writer Paul Logothetis in Curitiba, Brazil, contributed to this report