Switzerland caused a stir by beating one of the tournament favorites in its Group H opener. That result may have made advancing a bit more challenging for Chile.
Both teams will be looking for their second victory Monday in Port Elizabeth and a possible place in the knockout round.
The Swiss stunned Spain 1-0 on Wednesday despite getting outshot 24-8 by the reigning European champions. Midfielder Gelson Fernandes' goal off a scramble in the second half proved to be the difference as Switzerland used a strong defensive display to pull off the upset.
"We were fighting 95 minutes. We knew that Spain is a great team and we only have a chance if we work as a team,'' goalkeeper Diego Benaglio said. "We took our chance and now we are in a good situation."
Chile was impressive in its 1-0 victory over Honduras on Wednesday, with Jean Beausejour scoring and playmaking forward Alexis Sanchez turning in a commanding display.
The Chileans, though, were not happy with their output after a 20-7 edge in shots, and hope the lack of goals won't hurt down the road.
"We attacked well although we could have had a few more goals, and that might work against us in the final reckoning," coach Marcelo Bielsa said.
The winner will advance if the match between Spain and Honduras ends in a draw.
The Swiss will be without defender Philippe Senderos (ankle), and Steve von Bergen will replace him. Captain Alexander Frei and midfielder Valon Behrami are doubtful after missing the opener with leg injuries.
The health concerns have played into Switzerland coach Ottmar Hitzfeld's hands as far as convincing his team that it remains an underdog.
"We've known for a long time that the key match is Monday,'' von Bergen said. "Chile remains favorite for this."
Chile isn't willing to concede that point to the Swiss.
"I don't think there is a favorite for this match," goalkeeper Luis Marin said. "Both teams have got the same obligation to go out there and play like they did in the first match."
La Roja hopes to have striker Humberto Suazo available. Suazo scored 10 goals to lead all players in South American qualifying, and could be back from a left thigh injury.
Midfielder Jorge Valdivia, who was substituted in the 87th minute against Honduras after suffering a dead right leg, has been working apart from the other players in training. Valdivia appears to be progressing well.
"He's working almost at the same level as everybody else,'' defender Ismael Fuentes said. "He's very motivated to be able to play and the medical team is working with him to make sure he's fit."
These nations have met three previous times. The Swiss won 2-1 in the last matchup in a friendly in 2007, and Chile won the lone World Cup meeting in 1962 in Santiago.