Argentina were at full strength, on paper at least. Lionel Messi may not have been close to full fitness -- he had only played the last 15 minutes against Uruguay on Friday and looked short of his usual sharpness. And over the course of the game they lost Cristian Romero, their best centre-back, and midfield anchorman Leandro Parades to injuries. Lautaro Martinez also left the game at the interval. He may have been feeling a knock, but his replacement was also an admission by coach Lionel Scaloni that the game was not going as he had planned. An out-and-out centre-forward, Martinez was not able to get into the game because Brazil blocked Argentina in midfield so effectively.
Brazil were without both Neymar and Casemiro -- the players referred to by coach Tite respectively as the technical leader and the competitive leader. The attack was extraordinarily youthful; centre-forward Matheus Cunha was making his first start for the national team, Vinicius Junior his second and Raphinha his third. The other member of the attacking quartet, Lucas Paqueta, looks like a grizzled veteran in comparison, but he has only consolidated his place in the side over the last few months.
But with the wingers helping back, and full-backs Danilo and Alex Sandro playing conservative roles, Argentina were denied the space to establish their customary passing rhythm in midfield. In comparison with the final of the Copa America in July, it was clear that the extra speed of Eder Militao at centre-back allowed Brazil to stay compact higher up the field so they could press more effectively. And if the defensive line was breached, the immaculate Marquinhos was there to cover. Alisson in goal was hardly troubled. He had to dive left to push away a shot from Rodrigo De Paul, and, in the 89th minute, Messi finally broke away but struck straight at the keeper.
The clearer chances, however, came at the other end. Vinicius fluffed an audacious chip after a clever pass from Paqueta. Matheus Cunha was still more audacious, and shot narrowly over from inside his own half with Emiliano Martinez stranded. A Fred volley clipped the bar after a free kick had been half cleared, and a rare Danilo burst set up Vinicius for a shot that Martinez got down smartly to save.
There was, perhaps, little on show that will linger in the mind of the neutral. Maybe the venue did not help. The game was taken to the small northern town of San Juan, with the crowd close and creating a frenetic atmosphere. Argentina's usual home, River Plate's stadium in Buenos Aires, might have provided the stage for a more cerebral affair, with more light than heat. Bit ever here, there was something to be learned. Brazil have had cause for concern at a lack of emotional control -- they clearly did not do themselves justice when chasing the game in the final of the Copa America. Here they were tested, especially when Nicolas Otamendi got away with smashing a forearm into the face of Raphinha. But they were able to keep their cool -- just. And with plenty of attacking flair combined with a record of just four goals conceded in 13 qualifiers, they can build for the World Cup in confidence.
As can Argentina who, if not at their best on this occasion, have put together their most solid, coherent and frequently attractive side for the last few years. Their new total of 29 points guarantees their World Cup place because so many of the teams behind them dropped points -- including Chile, who went down 2-0 at home to Ecuador.
Everything went wrong for Chile in the first half. They went behind early to a well struck shot from rampaging left-back Pervis Estupinan. Soon afterwards they had Arturo Vidal sent off. And Alexis Sanchez limped off. They made a bold effort to haul themselves back into the game, but the points were sealed in stoppage time when midfielder Moises Caicedo advanced to score a cracker from the edge of the box.
Ecuador were the big winners of this round. They went into the action safely in third place, with a four point cushion, which has now been increased to six. Effectively this means that they are guaranteed to go into the final two rounds still in third place. A slot in Qatar is now theirs to lose.
Chile's defeat means that they fall from fourth to sixth, outside the qualification places. They are overtaken by Colombia, despite a deeply disappointing 0-0 draw at home to Paraguay. For both sides it was their fifth consecutive game without a goal. But Colombia have been defending so well that they have only lost one in their last 10, and are crawling to the World Cup one point at a time.
Into fifth, the playoff spot, climb Peru, who have made a remarkable rally since the Copa America in the middle of the year. Their 2-1 win away to Venezuela was open and dramatic, with the two sides trading punches. At 1-1 the game was decided by two set pieces. Peru won a free kick on the edge of the area, and Cristian Cueva's shot flicked off the defensive wall and beat the keeper. Straight away, Venezuela were awarded a penalty. Darwin Machis had already scored a fine goal, but his kick was at a comfortable height for Pedro Gallese to save. Gallese had more problems in stoppage time when a Machis shot took a deflection, requiring a fine reflex save. Such moments turned one point for Peru into three -- and the difference could well be vital when the competition comes to an end.
Peru are a point ahead of Chile, and of Uruguay, who found new ways to self destruct in their latest defeat, 3-0 away to Bolivia.
The extreme altitude of La Paz is an extremely tough challenge for visitors, and for almost half an hour Uruguay appeared to be taking the sting out of the game. But there are risks in defending deep, especially for the goalkeeper. At altitude, the ball flies through the rarefied air more quickly than usual, making it hard for the keeper to judge its trajectory.
Bolivia's veteran Juan Carlos Arce sent in a cross from deep on the left, looking for centre-forward Marcelo Martins Moreno. He stretched but was unable to make contact. Uruguay keeper Fernando Muslera had to prepare to cover his shot, and when the ball went straight on it came at him quicker than he expected, slipped through his hands and tricked in off the far post.
Then, just before half-time, Uruguay needlessly gave away a corner. Their marking was slack, and Martins Moreno rose to give Bolivia a two goal lead and put Uruguay in the dreaded position of having to chase the game while gasping for oxygen. They lost 3-0, a result that keeps Bolivia's hopes alive, but which may well bring an end to the remarkable near-16 year reign of Uruguay coach Oscar Washington Tabarez.