Mexico was on the brink of an early exit from the Under-20 World Cup after losing 1-0 to Paraguay on Tuesday, while newcomer El Salvador stunned Australia 2-1.
Colombia, meanwhile, got its campaign on track with a 1-0 win over host Turkey. The victory moves the South American champions to the top of Group C following a disappointing opening draw against Australia. The win also denied Turkey an early chance to advance.
Paraguay, which drew its opening match against Mali, made the breakthrough in the 52nd minute when substitute Arnaldo Sanabria fed Derlis Gonzalez, who scored with a superb side-footed volley.
As the CONCACAF champion, Mexico and its potent attack featuring Jesus Corona and Marco Bueno had been tipped as one of the tournament favorites. But it has struggled to perform in Turkey and Tuesday's match was no different. It missed several good chances - hitting the post twice, including with a free kick from Jorge Espericueta in the final minute.
Having lost 2-1 to Greece in its previous game, Mexico finds itself bottom of Group D with a match against Mali remaining. Paraguay and Greece lead the group with four points after the Greeks drew 0-0 with Mali to also miss out on an early chance to qualify for the next round.
In Group C, El Salvador improved its chances of advancing with a victory that put its first points on the board.
Australia, which had earned a deserved 1-1 draw against fancied Colombia, started well with Joshua Brillante putting the young Socceroos ahead in the ninth minute.
But El Salvador, which lost 3-0 to Turkey in its opener, drew level just eight minutes later. Jairo Henriquez delivered a deep cross which Kevin Barahona headed back across goal and into the path of Diego Coca, who scored.
Jose Pena provided the winner in the 40th, steering home a low cross from Miguel Ochoa.
After an uneventful first half, Turkey went on the attack and nearly scored courtesy of a dipping, swerving free-kick from about 30 yards (meters) by Hakan Calhanoglu.
But Colombia responded in style, with Juan Quintero twisting and turning just inside the area and then firing a blazing shot into the roof of the net in the 52nd.
Quintero nearly scored again a few minutes later when the midfielder beat keeper Aykut Ozer with another left-foot shot - only to see it cleared off the line by Ilkay Durmus.
