The World Cup qualifiers return this week with a plethora of major matches for some of South America's major clubs.

Entering the tournament, Chile, the Copa America Champion, was initially seen as a favorite to ride into the next World Cup, alongside the likes of Colombia, Argentina, Brazil and Uruguay.

Yet, four games into the tournament, the race is as tight as ever, with a few top dogs barely holding on.

Argentina and Chile Lock Horns Despite Struggles

Argentina's story is undeniably the most fascinating. The superstar squad, led by Lionel Messi, only gathered five points through six matches. Despite stars such as Angel Di Maria, Sergio Aguero and Messi leading the charge, the team's offense has stalled, scoring only two goals in its four matches and acquiring just one victory in that span.

Now the team takes on Chile, the defending South American champs who have seven points and are currently clinging to the wild card spot in the standings. Chile got off to a tremendous start, winning their first two games in emphatic manner, before a questionable defensive line started to plague them. The team is winless in their last two qualifiers, despite taking down Brazil 2-0 in their opener.

Chile will be home and are the favorites. A win puts the team right back into the conversation for a top spot, while a loss puts it on the outside looking in. Argentina needs a win as well. A defeat would keep the team below the line through the summer and into the fall.

Colombia's System Needs Change

The Colombians entered the qualifiers with a bright future. The Copa America was an unmitigated disaster for the team due to a lot of missing pieces, but some felt that the squad would return to their best in the World Cup qualifiers.

That has been far from the case. Colombia scraped out a win at home against Peru, despite being outplayed, before getting destroyed by Uruguay on the road and by Argentina at home. The draw against Chile was a saving grace, but even there Colombia was putrid.

The offensive system has not been particularly sound lately. Jose Pekerman opted for a more possession-based approach that has not worked out for the speedy but not technically-proficient Colombians. James Rodriguez's fall from grace has not helped matters either.

Colombia is set for a game with Bolivia in La Paz, arguably the toughest place to play in the qualifiers. The team needs a big game or could continue to struggle.

Los Cafeteros are currently three points out of a qualifying spot, but even with a win here they may not ultimately move on. A loss could spell the end for Colombia's campaign.

Brazil Faces Toughest Team

Ecuador may be riding high, but anyone paying attention knows that Uruguay is the team to beat. The squad was firing on all cylinders through four games, even without their top player, Luis Suarez.

Now Suarez is set to return, and those who have seen the superstar know that he is the most dangerous goal scorer in the world at the moment.

This is bad news for Brazil, who have looked unconvincing thus far in the qualifiers. Their most recent win over Peru was huge for the team, but there are lingering questions over defensive form, as well as Neymar's integration into the squad. The captain has yet to show his most potent playing in his national colors, and his play could be the difference in this matchup between two giants.

A win for Uruguay would put the nation closer to solidifying its position, while putting Brazil in a bad spot, depending on how other games break. A Brazilian win would put the Selecao ahead of Uruguay, while leaving both sides in qualifying positions. A draw would be good for Uruguay, but precarious for Brazil.