Birthday boy Lionel Messi will go for goals while France fight to prove that South America will not get everything its own way in Wednesday's key World Cup games.
The penultimate day of group games sees three round of 16 places decided.
Messi's Argentina play Nigeria in Porto Alegre at 1600 GMT having already qualified from Group F but needing one point to make sure of top spot. They also need to reassure fans about their lack of goals so far.
A draw would also be good enough for Nigeria to go through, but Iran will be looking for goals and hoping the Africans slip up, when they play Bosnia-Hercegovina in Salvador at the same time.
In Group E, free-scoring France need a draw against Ecuador to guarantee top spot in their Rio de Janeiro game at 2000 GMT. Switzerland will also be looking to claim a place when they play Honduras at the same time in Manaus.
Argentina's Messi marked his 27th birthday on Tuesday with messages from adoring fans and top personalities. Among them was Argentina coach Alejandro Sabella who admitted there is a "dependency" on the Barcelona striker.
In Argentina's games so far against Bosnia and Iran, it has taken Messi brilliance late in the game to break a worrying deadlock.
"There is huge pressure on him, it's normal, but we try to take some off his shoulders," said Sabella who will be hoping for a more convincing performance this time in front of another stadium packed with Argentine fans.
If Argentina win 1-0 again and Iran win by the same score, FIFA may have to draw lots to decide the second place from the group as Nigeria and Iran's points, goal difference and head-to-head records will be identical.
- Europe hammered -
After Spain, England and Italy crashed out of the tournament, Europe's hopes of success rest on a shrinking base including France.
A win over Ecuador could help eliminate a South American team for a change.
France have scored eight goals in two games so far -- three from Karim Benzema -- and coach Didier Deschamps has pressed his side to "maintain everything we have done so far and finish the job."
Deschamps could bring in Southampton midfielder Morgan Schneiderlin for suspended Yohan Cabaye.
Ecuador are currently ahead of Switzerland in second place on goal difference. Coach Reinaldo Rueda is looking for inspiration from other South American teams -- Brazil, Argentina, Uruguay, Chile and Colombia -- who have already qualified.
"We hope to follow in their footsteps," he said.
Switzerland also have a score to settle against South American opponents when they play Honduras to make sure they get second place.
At the 2010 World Cup, Switzerland were also in contention for the last 16 but could only draw with Honduras.
"Everyone can nurture big dreams, but first we have to do a little homework and that is to beat Honduras," said Swiss midfielder Blerim Dzemaili.
Honduras have not made it out of the group stages in two previous trips to the World Cup finals.
Los Catrachos will need an avalanche of goals against the Swiss, and hope that France beat Ecuador to make it this time.