Argentina's Pablo Bouza moves in to tackle Paddy Wallace
Argentina (6) 22
Pens: Contepomi 4
Ireland (10) 20
Tries: Carney, penalty
Con: Wallace 2
Pen: Wallace, Duffy
A late drop-goal by Leinster fly-half Felipe Contepomi denied Ireland a first ever victory on Argentine soil.
Eddie O'Sullivan's men, who had led from the sixth minute, looked set for a win after a penalty try followed debutant Brian Carney's touchdown.
But Contepomi's boot kept the Pumas in touch and then Hernan Senillosa's try helped edge Argentina ahead.
With Paddy Wallace off injured, Gavin Duffy restored the Irish lead with a penalty but Contepomi snatched the win.
Former rugby league star Carney had a dream start to his first match in an Ireland jersey.
The Munster man intercepted a Contepomi pass to race clear to score under the posts.
Ulster's Wallace, having opened the scoring with a penalty, added the conversion to put Ireland 10-0 up after nine minutes.
Contepomi, though, landed two penalties to peg the gap back to 10-6 by the interval.
We played well but discipline was the problem
Ireland coach Eddie O'Sullivan
The home number 10 added another penalty to reduce the deficit to a single point but the penalty try saw the Irish establish a 17-9 advantage.
Contepomi's fourth penalty and Senillosa's converted try had Argentina 19-17 ahead.
Full-back Duffy drilled over Ireland's last score but it was not enough as that man Contepomi grabbed his chance with the match-winning drop in the 80th minute.
"It's unusual for me to take drop-kicks but it was something we worked on and it came off," Contepomi said later, insisting: "It would have been unfair if we had lost".
"We dominated the game for long periods despite being behind for almost the whole game."
Ireland coach Eddie O'Sullivan highlighted a lack of discipline as the main reason for his side's defeat.
"I talked to the players and said they played well but discipline was the problem," he said.
"We gave away too many penalties, especially in the second half.
"In the first half, we were controlling the game. Argentina took the upper hand after the break and took their opportunities very well. But in the end either side could have won it."
Argentina: B Stortoni; T de Vedia, M Avramovic, H Senillosa, F Leonelli; F Contepomi (capt), N Vergallo, JM Leguizamon, J Fernandez Lobbe, M Durand, E Lozada, P Bouza, S Gonzalez Bonorino, A Vernet Basualdo, M Ayerza.
Replacements: Cardinalli for Bonorino (76), Fessia for Durand (71).
Ireland: G Duffy; B Carney, A Trimble, K Lewis, T Bowe; P Wallace, I Boss; B Young, J Flannery, S Best (capt), T Hogan, M O'Kelly, N Best, K Gleeson, J Heaslip.
Replacements: O'Leary for Bowe (80), G. Murphy for Wallace (63), Buckley for Young (66), Jackman for Flannery (78), O'Driscoll for Hogan (23), Ferris for Gleeson (71).
Referee: Lyndon Bray (New Zealand)