Spain take on the dark-horse South American side in Rio de Janeiro, while Group B leaders the Netherlands look to score more goals against Australia in Porto Alegre. Cameroon play Croatia in the third match of the day in Manaus at 2200 GMT.
After their 5-1 hammering by the Dutch on Friday, Spain know that only a win will do. Vicente del Bosque's side will be eliminated if they lose to the Chileans and the Dutch avoid defeat.
"We'll have to fight one against one," said star midfielder Andes Iniesta.
Del Bosque has hinted at changes to the team. Goalkeeper and captain Casillas, who took the blame for the defeat, has however been given public support by the coach who insisted the whole team should be scolded.
Chile, who play an aggressive attacking game, will be looking to Barcelona forward Alexis Sanchez to put more pressure on whoever starts in goal for Spain.
Coach Jorge Sampaoli has doubts over Juventus midfielder Artur Vidal however.