Argentina's hopes of sealing qualification for next year's World Cup were thwarted in a 1-1 draw with Ecuador on Tuesday as Colombia took a massive stride towards the finals in Brazil with victory over Peru.
The Argentines, who once again left Lionel Messi on the bench, had to settle for a point after Segundo Castillo cancelled out Sergio Aguero's early spot kick for the visitors at the Olympic Stadium in Quito.
Ugly scenes marred the closing stages, with Argentina captain Javier Mascherano sent off for kicking a medic who was stretchering him off the pitch in an incident that triggered a prolonged touchline melee.
Argentina coach Alejandro Sabella praised the performance of his side in digging out a point against an Ecuador team who had boasted a 100 percent record in previous home qualifiers, all staged 2,800 metres above sea level.
"We knew it was going to be our hardest game," Sabella said. "We had a lot of things against us -- injuries, suspensions. But the team responded with great dedication. I am very satisfied."
Argentina could have wrapped up qualification with a victory but nevertheless should reach Brazil comfortably with three games remaining.
However Sabella warned against complacency ahead of their next fixture against Paraguay in September. "We're not qualified until it's mathematically certain," Sabella said.
Argentina were given a dream start after only four minutes when Manchester City striker Aguero fired the visitors ahead.
Ecuador goalkeeper Alexander Dominguez was the villain for the home side, spilling Angel Di Maria's long-range effort before clumsily bundling over Rodrigo Palacio as the Inter Milan forward pounced on the rebound.
Aguero made no mistake with the subsequent spot-kick, sending Dominguez the wrong way to put Argentina 1-0 up.
But Ecuador were back on level terms after 17 minutes. Ecuador captain Walter Ayovi whipped in a free-kick from the left and Castillo slipped his marker to thump home an unstoppable header from close range.
The Ecuador equalizer appeared to sap morale from the Argentine ranks, and they found themselves firmly on the back foot for much of the remainder of the contest.
The introduction of Messi from the bench on 61 minutes raised Argentine hopes but the Barcelona maestro was unable to break the deadlock.
The result left Argentina on top of the nine-team South American zone qualifiers with 26 points from 13 games, with three matches left to play.
Ecuador are third in the standings with 21 points after 12 games.
Second-placed Colombia edged towards their first World Cup finals appearance since the 1998 tournament in France with a clinical 2-0 win over Peru in their port stronghold of Barranquilla.
Colombia took the lead after 13 minutes when Monaco striker Radamel Falcao coolly converted from the penalty spot after Napoli winger Juan Zuniga had been bundled over by Victor Yotun for a clear foul.
Teofilo Gutierrez made it 2-0 on the stroke of half-time to put Colombia on the threshold of World Cup qualification.
In other games on Tuesday, a goal from Napoli's highly rated striker Edinson Cavani breathed life into Uruguay's faltering qualification campaign to clinch a 1-0 win over Venezuela in Puerto Ordaz.
Cavani, reportedly a transfer target for Chelsea, Manchester City and Real Madrid, struck in the 28th minute for a win which lifted the 2010 World Cup semi-finalists into the qualification places.
Elsewhere Chile closed in on one of the four automatic qualifying berths with a 3-1 win over Bolivia in Santiago which came courtesy of goals from Eduardo Vargas, Alexis Sanchez and Arturo Vidal. Marcelo Martins got Bolivia's goal.
Victory saw Chile go level on 21 points with third-placed Ecuador, who they trail by goal difference. Chile are five points clear of fifth-placed Uruguay.
The top four teams automatically qualify for Brazil, with the fifth placed team facing a play-off against their Asian counterpart.