It was O'Gara's seventh successful attempt from seven efforts - two drop-goals and five penalties - but the overall control he exerted, particularly in the second half, laid the foundation for this win.
Argentina took the lead as early as the second minute when Felipe Contepomi, wind assisted, landed a penalty and he had a simple task to add the points when Federico Martin Aramburu got on the end of a good Manuel Contepomi break to score under the posts.
O Gara registered Ireland s first score with a neat drop-goal in the 8th minute but Contepomi re-established his side s 10 point cushion with a second successful penalty three minutes later. O Gara and Contepomi swopped penalties at the end of the opening half to leave the Irish in a good position, trailing 16-6, as they turned for the second half with the freshening wind at their backs.
A 46th minute O Gara penalty was cancelled by one from his opposite number two minutes later and then a sublime Brian O Driscoll break might have yielded a try had support arrived before he was tackled.
When Argentina rumbled their way into the Irish half, O Gara invariably booted them back downfield. From one such turnaround he kicked his third penalty to bring Ireland to within four points (19-15) and in the 71st minute his fifth successful penalty made it a one point game. That score came from a penalty award that saw Gonzalo Longo yellow-carded and the Pumas were left to fight a rear-guard action with just 14 players.
And they made a good fist of it for almost all of the final ten minutes until O'Gara coolly and clinically drilled over the winning effort.