Argentina and Chile both face defining World Cup Qualifiers over the next seven days that will determine whether Lionel Messi and Alexis Sanchez feature for their respective countries at next summer's tournament in Russia.
Meanwhile Chile, currently sitting sixth in the CONMEBOL standings, take on eighth-placed Ecuador in Santiago on Friday and Juan Antonio Pizzi's side then complete their qualifying campaign with a daunting trip to already-qualified Brazil on October 11.
Only the top four teams in the group automatically make it to Russia 2018, with the side in fifth facing a two-legged play-off against Oceania winners New Zealand in November.
However, given their recent patchy form, neither the 2014 World Cup finalists nor the reigning Copa America champions will be confident of competing at the global showpiece event.
Argentina - who sit fourth in the latest FIFA world rankings - head into their key double header having won just two of their last nine qualifiers and face the ignominy of missing out on the World Cup finals for the first time since 1970.
Jorge Sampaoli's side were grateful to a second-half own goal that helped them steal a 1-1 draw against already-eliminated Venezuela in the Argentina capital last time out.
But with the two-time World Cup winners having managed only 16 goals so far in qualifying, the second worst in South America and fewer than even defensive-minded Paraguay have scored, the pressure is once again on Messi to deliver.
Sampaoli - Argentina's third coach already in qualifying after Gerardo Martino and Edgardo Bauza - is expected to keep faith with his eye-catching front three of Messi, Paulo Dybala and Mauro Icardi against Peru on Friday.
"It's difficult to remove this 'Messi-dependency' from a team when Leo is there. When you know you have the best player you will always look toward him," Sampaoli said.
However, Sampaoli will be praying that his forwards are more clinical than they were in their last qualifier against Venezuela, when wasteful finishing in the first half was to blame for two costly dropped points.
"We have two games left against Peru and Ecuador and we need to win both of them," Sampaoli said after his team were held at home by the bottom side in the section.
"We had three chances to score in the first half and everything could have been settled. We must continue to fight in attack and give strength to the players."
"We let an important chance slip but this if football and these things happen. When you have 11 chances on goal and don't score, it's confusing.
"Now things are more complicated because we thought we would be in automatic qualifying places after this round of matches."
The worry for Argentina, however, is their next opponents have won their last three matches in a row, a run that has seen in-form Peru move into the fourth and final automatic qualifying position for next summer's finals.
Not only that, but Argentina then face a final-day visit to Ecuador who, despite losing at home to Peru last time out, possess an intimidating record in Quito.
Argentina have tended to struggle when playing at altitude, with Ecuador's ground in the capital situated 9,127 feet above sea level.
One piece of good news for Sampaoli and Co, though, is that rivals Chile and Ecuador play each other this week, while Paraguay, in seventh, also have a tough encounter at third-placed Colombia.
After entertaining Ecuador, Chile may then need to get a result in Sao Paulo against group leaders and five-time world champions Brazil to ensure their safe passage to Russia 2018.
Pizzi's team, though, head into those two critical fixtures on the back of successive defeats in qualifying, a 1-0 loss to Bolivia in La Paz that followed their surprise 3-0 home reverse against Paraguay.
And the La Roja head coach echoed his Argentina counterpart's sentiments after those damaging back-to-back setbacks in September.
"We will fight, we will make the greatest effort possible, we believe that we have the ability to compete with the best and we will try to obtain the results that allow us to qualify," said Pizzi.
"There are two matches left, I'm going to fight and my players are going to fight, with all the force we have."
Pizzi will be relying heavily on Alexis for Chile's final fixture with Brazil, although just what state of mind the Arsenal forward will be in for that clash is open to debate after the recent criticisms he has received.
La Tercera newspaper, in particular, questioned the player's performance against Bolivia, writing: "In La Paz, he extended the insignificance he had against Paraguay. He never understood how the game had to be played.
"To make matters worse, he got a yellow card that leaves him out of the game against Ecuador."
El Grafico Chile, meanwhile, commented: "Completely disconnected, lost in La Paz."
Sanchez hit back, however, writing on his Instagram account: "AND THE TIME COMES WHEN YOU GET TIRED. Tired of being criticised with and without a reason, tired that they want to see you defeated, tired of telling yourself 'once more I will get up' after crying following a defeat and you are tired of telling the world and those people around you that all is well.
"And worst of all is that no one realises how that makes you feel....I wear Chile's number 7 jersey and that brings an enormous responsibility, that is why I'm sad that journalists and bad people criticise without knowing..."
Sanchez and Co, though, maybe taking on a second-string Brazil side next week that have already sealed top spot in the CONMEBOL standings, so offering up the prospect of the Selecao inadvertently helping Chile into the play-offs at arch rivals Argentina's expense.
Either way, neither team should be fearing that prospect given New Zealand failed to pick up a point at last summer's Confederations Cup and lost 9-3 on aggregate to Mexico in the play-off to qualify for the last World Cup.