It was frenetic stuff as the match went one way and then the other and Hernandez' excellence at drop goals saw the Pumas go back into the lead shortly afterwards.
Hernandez beat Murphy to his up-and-under inside Irish territory that effectively set up the Pumas second try, which Agulla gleefully scored in the corner.
Contepomi converted to make it 18-10.
Argentina struck first in the second-half and all but ended Irish dreams when Contepomi converted a penalty after Simon Easterby was penalized for pulling down a maul.
However, the Irish had other ideas and a brilliant passing move down the backline saw Murphy -- controversially dropped by O'Sullivan from the 22 for the 25-3 defeat by France -- run in unopposed to touch down.
O'Gara failed to convert to leave Ireland trailing 21-15.
Contepomi had his kicking back on track and the qualified surgeon showed his precision-like skills as he landed a penalty in the 62nd minute to make it 24-15.
He was back to turn the screw on the Irish two minutes later and made it 27-15, while O'Sullivan resorted to his last hope by sending on four replacements in a desperate search for a miracle.
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