Colombia fought back with striker Radamel Falcao converting two late penalties against a Chile side inspired by Alexis Sanchez's first-half brace for a 3-3 draw and the point that put them in their first finals since 1998 with a match to spare.
"I was surprised by what happened to us ... it could have been due the pressure accumulated over a long time," said Colombia's coach Jose Pekerman after his side, who had won five home qualifiers in a row, conceded three goals in the opening half hour before fighting back.
"I'm very proud of my team, I've rarely seen a national team in this kind of match get back from 3-0 down," the Argentine said.
Chile's coach Jorge Sampaoli, said: "Bitter about the final result, given how things went in the first half, and now hopeful going to seek the match that will give our qualification."
Chile went ahead with a penalty by Arturo Vidal in the 19th minute after striker Eduardo Vargas was brought down.
Sanchez then scored twice in seven minutes to stun the Colombians and put Chile three up inside the opening half hour.
With Chile having lost Carlos Carmona to a red card in the 66th minute, Teo Gutierrez pulled one back in the 69th and fellow striker Falcao added two penalties in the last 15 to secure Colombia the point they needed.
Montero put Ecuador ahead when he ghosted in behind Maxi Pereira to steer the ball home as goalkeeper Fernando Muslera failed to cut out Antonio Valencia's cross.
In Quito, Jefferson Montero scored on the half hour to give Ecuador a 1-0 home win over Uruguay and climb to third in the South American group behind leaders Argentina, who qualified last month, and Colombia.
The Ecuador team did a lap in honour of their late team-mate Cristian Benitez, who died suddenly of heart failure in July.
Venezuela's slim hopes of going to the finals for the first time ended in a 1-1 draw at home to Paraguay, while a rampant Argentina, without Lionel Messi and Gonzalo Higuain, beat Peru 3-1 in Buenos Aires with Ezequiel Lavezzi scoring twice after Claudio Pizarro's fine 21st-minute opener for Peru.
The fifth-place play-off berth has become a Uruguay fixture at the last three World Cups with them qualifying that way in 2002 and 2010, when they went on to reach the semi-finals, though they lost to Australia in the play-off in 2006.
Finishing fifth will put them into a two-legged play-off against Asian qualifiers Jordan next month.
The defeat in Ecuador where Luis Suarez, joint top scorer with Messi in the group with 10 goals, came closest to an equaliser with a dipping free kick has left Uruguay with a tough task on Tuesday to beat Argentina by a big score in a bid for an automatic ticket.
A draw in Santiago, where Chile host Ecuador, will ensure both take the last two automatic places in Brazil.
Ecuador have a goal difference of plus five, Chile plus three and Uruguay, who are three points behind them both, minus one.
Going into Tuesday's last round of the marathon 16-match group, Argentina have 32 points, Colombia 27, Ecuador and Chile 25 and Uruguay 22.