This all would have been far simpler had Colombia not collapsed in the last five minutes at home to Paraguay. Ahead by the only goal, the Colombians already were celebrating having qualified, and the Paraguayans appeared to have no chance. But history teaches time and again that they should never be written off, and their two late goals have thrown extra confusion into the mix. Although they currently lie seventh, Paraguay have a great chance to climb two places in the table.
ECUADOR vs. ARGENTINA
This is the match that will command most of the world's attention. It is possible that Argentina could lose and still make the playoff spot. But it is probably more likely that even a draw would eliminate them and possibly bring an end to the international career of Lionel Messi.
So the stakes are high -- and so is the venue. Ecuador play their matches at Quito, 2,850 metres up the Andes. Argentina detest these conditions. Altitude is hard for all unacclimatised visitors. The lower oxygen level in the air makes breathing difficult, and playing a normal game impossible, and the Argentines usually have huge problems adjusting.
But there is some good news for Messi and company. The early leaders, Ecuador are in disarray. They are on a run of five consecutive defeats and have recently sacked their coach. Caretaker boss Jorge Celico has gone with an experimental squad, leaving out some of their seniors and giving a chance to more domestically based players.
In front of their own fans, Ecuador likely will look to attack, seeking to redeem some honour after the recent reverses. This has not happened to Argentina for a long time. Their last three matches, all drawn, have come against opponents who rarely ventured out of their own half, and whose main aim was to frustrate and run the clock down. Now, at last, there should be some space for Messi and his supporting cast to work in. For all their problems, Argentina's fate remains in their own hands.
PARAGUAY vs. VENEZUELA
With the Paraguayans playing the final round at home against the team on the bottom of the table, a win probably would be enough to guarantee fifth place.
But Paraguay's task is more complicated than it might appear, for two reasons. First, Venezuela are on a high, boosted by their splendid recent under-20 World Cup campaign and building optimistically for the future. Coach Rafael Dudamel also has been celebrating the team's recently acquired defensive solidity -- the last three games have been draws against Colombia, Argentina and Uruguay, with just one goal conceded.
Then there are the characteristics of Paraguay. There is a reason for the striking fact that the team has won more away games than home. Paraguay seek to defend deep, hang on with legendary resilience and then break out at pace. It is a model of play best suited to road games, where the opponent more often pushes forward and they have space to launch a counterattack. At home, denied such space, they can be laboured and unimpressive -- and dealing with the pressure of the occasion will not be easy.
But if Paraguay can claim three points, it puts real pressure on the teams who disputed the last two continental titles, Chile and Argentina.
BRAZIL vs. CHILE
Like Argentina, Chile have control of their future -- but their task is even harder. Their final game is away to Brazil, who are in exceptional form. The Brazilians have never lost a World Cup qualifier on home soil, they will be saying farewell to their fans and they are seeking to retain their intensity and avoid falling into the trap of peaking too soon. Moreover, Chile have key midfielder Arturo Vidal suspended, and will probably be missing Charles Aranguiz through injury.
The campaign started with Chile beating Brazil 2-0 in Santiago. It was a beautiful moment for the Chileans. They recently had been crowned continental champions, and had overcome everyone apart from Brazil -- who knocked them out of the last two World Cups. That win, more than two years ago, was a very sweet moment. To win away from home would be sweeter still. A draw should be enough to secure fifth place, but even that looks like a tall order.
PERU vs. COLOMBIA
The very first game of the campaign was Colombia's 2-0 win over Peru in Barranquilla. The Colombians were flattered by their win. Peru deserved a draw, but their dismal away record continued. Their last win on the road in World Cup qualification had come in 2004, and they had barely picked up as much as a draw since then.
More than two years later, Colombia continue to disappoint. Consistently there is the feeling that there is more to come from Colombia, that if they get their act together they are capable of at least equalling their 2014 World Cup run, when they made their quarterfinal debut. Coach Jose Pekerman has had a strange campaign, using 45 players, seemingly never entirely sure of his team and uncertain in his substitutions.
Peru, meanwhile, have gone through a significant evolution. Coach Ricardo Gareca has demonstrated faith in a new generation of players and, with plenty of patience being shown along the way, the policy seems to be working. In the seven games played over the last 12 months, Peru have suffered just one defeat, and have put together four wins, two of them coming on the road.
But can they do it now at home? The pressure is on. Peru have not been to a World Cup since 1982, and a draw may not be good enough -- though it almost certainly will guarantee at least the playoff spot for the Colombians. And how will the Colombians react after the events of last Thursday, when they were less than five minutes away from automatic qualification before their sudden collapse against Paraguay?
The mental aspect will be immense in the crunch tie of the round -- the only one where there is something at stake for both teams. Peru against Colombia, then, is a fitting finale to a dramatic campaign.