Argentina are in danger of missing a first World Cup since 1970 after being held to a goalless draw by Peru.
Only the top four in South American qualifying are guaranteed a place at the 2018 tournament in Russia, and Argentina are sixth with one game left.
The two-time World Cup champions must win their final qualifier in Ecuador to claim at least fifth spot which sets up a two-leg play-off against New Zealand.
The final round of games kick-off at 00:30 BST on Wednesday, 11 October.
Argentina coach Jorge Sampaoli conceded “the situation is not comfortable” but added he was “confident that if we play with the conviction with which we did against Peru we will be in the World Cup”.
Lionel Messi hit the post in the second half and Sampaoli praised the Barcelona forward’s “great intensity” as he created numerous opportunities that his team-mates were unable to convert in front of a 49,000-capacity crowd at La Bombonera in Buenos Aries.
Argentina, beaten finalists at the 2014 World Cup, are level on both points (25) and goal difference (+1) with fifth-placed Peru, who are ahead on goals scored.
So tight is the group that four points separate Uruguay in second (28) and Paraguay (24) in seventh and a win for Argentina could see them qualify automatically.
However, they have drawn their past three qualifiers and their recent record in Ecuadorian capital Quito, which is 2,900m above sea level, is poor, losing two out of their past three and drawing the other. Ecuador have lost their previous five qualifying games.
Peru are hosting fourth-placed Colombia and should they draw, Argentina would be eliminated if they did not win.
Chile, who are third, go to already-qualified Brazil, while Uruguay, who are all-but assured of their place in Russia because of their vastly superior goal difference, need just a draw at home to already-eliminated Bolivia to guarantee qualification.