Argentina once again required heroics from their talisman Lionel Messi as the diminutive forward scored an injury-time winner to secure qualification from World Cup Group F and break the hearts of a dogged Iran.
Having inspired his side to victory after a below-par performance in their opening fixture against Bosnia-Herzegovina, the Barcelona man bent home a decisive goal in the dying embers of a game in which the hard-working Iranians did enough to deserve all three points.
Both goalkeepers looked to be unbeatable as Sergio Aguero had Argentina's best chance and Reza Ghoochannejhad came close on more than one occasion for the underdogs, who also saw a strong penalty claim turned down.
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Jalal Hosseini could not connect with an early Iran free-kick into the Argentina box as Carlos Quieroz's Iran looked to take an early shock lead and lump pressure on their high-profile opposition.
Gonzalo Higuain and Fernando Gago had come into the side after their second-half influence from the bench in the win over Bosnia-Herzegovina, and the duo combined to create the best chance for Alejandro Sabella's team in the opening 15 minutes.
Gago played Higuain through on goal but saw his shot smothered by Alireza Haghighi, who showed quick reactions to race from his line.
Angel Di Maria was the next to try his luck but he could only bend an effort well over the crossbar, with Manchester City forward Aguero forcing an athletic save from Haghighi and Marcos Rojo heading wide as Argentina began to dominate proceedings.
With Iran only breaking free on rare occasions, Garay was the next to pass up a good opportunity as he headed over from close range under no pressure.
Having been left frustrated by a stubborn Iran in the opening 45 minutes, the second half started in a similar fashion for the South Americans, with Pablo Zabaleta curling a shot wide after being picked out by Messi.
Aguero could not make enough contact with a Rojo cross before Iran hit on the counter-attack and Ghoochannejhad's headed attempt forced Sergio Romero into a low save.
Iran could have easily been awarded a penalty moments later as Zabaleta mis-timed his challenge on Ashkan Dejagah, with referee Milorad Mazic unmoved as the Fulham winger protested aggressively.
Those scares seemed to spring Argentina back into life, with Messi sending a shot wide of the post after some good work, but Iran maintained their new-found threat as Ehsan Hajsafi let loose from distance.
Romero then made the save of the game as he was at full stretch to turn Dejagah's goalbound header over his crossbar.
The game was becoming stretched and Messi again came close but could only hit the side netting from a free-kick.
Sabella gambled with under 15 minutes remaining as he replaced Aguero and Higuain with fellow attackers Rodrigo Palacio and Ezequiel Lavezzi.
Palacio saw a near-post header turned behind for a corner with Iran now pinned back in and around their own penalty area.
With just four minutes remaining, Iran dealt with another corner and Ghoochannejhad was played in behind the Argentina defence but the Charlton striker could not keep his shot away from Romero.
That miss proved costly as Messi took centre-stage, receiving the ball from Zabaleta and showing great composure to curl a shot perfectly out of the reach of Haghighi and into the corner of the net.
The goal means Argentina are guaranteed a place in the knockout stages, while Iran remain on one point with just one group game remaining.