The once unfathomable prospect of a World Cup without Lionel Messi and Argentina could become reality on Tuesday as South America's thrilling 2018 qualification battle reaches its climax.

Two years after Argentina kicked off their troubled campaign with a 2-0 defeat at home to Ecuador, Jorge Sampaoli's side travel to Quito to face La Tri once more with their hopes hanging precariously.

The two-time World Cup-winners head into the final round of games in sixth place overall, outside the top four positions which grant automatic qualification and trailing fifth-placed Peru, who occupy the playoff spot, on goal difference.

Yet with only two points separating third-placed Chile (26 points) with seventh-placed Paraguay (24), any number of permutations are possible.

Argentina can simplify the equation for their fans, however, if they manage to take all three points.

A victory would guarantee they finish no worse than fifth place, putting them into a two-legged play-off against New Zealand they would be expected to win.

But achieving victory in the thin air of Quito, which is 2,850 metres (9,350 feet) above sea level, may be easier said than done.

The Argentinians have an abysmal record in away games against Ecuador, with their last victory in Quito coming in 2001.

Since then in World Cup qualifying games, they have been beaten twice, in 2005 and 2009, before scraping a 1-1 draw in 2013.

Moreover, Argentina face their moment of truth after a series of uninspiring performances that has left the rest of the footballing world scratching its head at how a squad bristling with so much attacking talent has found scoring so difficult.

- 'Hanging on' -

Despite being able to call upon Messi, Sergio Aguero, Gonzalo Higuain, Paulo Dybala, Mauro Icardi and Angel Di Maria throughout the campaign, Argentina have only scored 16 times in 17 games.

Last Thursday's 0-0 stalemate with Peru in Buenos Aires was Argentina's third consecutive draw. The Albiceleste have now scored only once in their past four qualifying games.

Sampaoli attempted to break that cycle last week with the surprise selection of Dario Benedetto in attack, a gamble that failed to pay off after the Boca Juniors striker missed a string of chances.

It is unclear whether Sampaoli will persist with Benedetto again on Tuesday.

While Messi and his team-mates attempt to adjust to the lung-busting challenge of playing at altitude, millions of compatriots will be holding their breath.

The sense of anxiety was reflected by La Nacion newspaper. "Argentina is not on the edge of the precipice - it is hanging on the cornice vertically," the paper commented.

Elsewhere on Tuesday, Chile could seal their qualification with victory over Brazil in Sao Paulo. Brazil have already qualified for the finals and are guaranteed top spot.

Uruguay meanwhile need only take a point in their home qualifier against already-eliminated Bolivia to be certain of progressing.

One of the most high-stakes games comes in Lima, where Peru will aim to qualify for their first World Cup finals since 1982 when they take on Colombia.

Colombia were moments from qualifying for the World Cup last Thursday before two last-gasp goals from Paraguay turned a 1-0 win into a 2-1 defeat.

That win kept Paraguay's qualification bid alive and a home win over Venezuela on Tuesday could see them seal their place to Russia depending on results elsewhere.