Argentina 15-16 Ireland
Ireland made heavy weather of beating Argentina but can now look forward to the knock-out stages of the World Cup.
In a must-win match for each team, Ireland sneaked home by one point having scored the only try of the match.
Argentina now return home after a disappointing campaign that promised much but resulted in defeats when it mattered most.
It never mattered more than this match which was tight and tense throughout. What it lacked in quality it more than made up for in excitement.
Alan Quinlan crossed midway through the first-half for the game's only try, but his effort failed to ignite the Irish.
They played second fiddle to their opponents for large parts of the game, only coming to life in the final quarter after Ronan O'Gara replaced David Humphreys at fly-half.
Even then it was a stop-start performance, but O'Gara did the basics with aplomb, kicking his penalties and finding touch.
He also injected some pace and invention into a previously sedate Irish backline, although the men outside him could just as easily point to fear being their motivation.
Ireland were knocked out of the last World Cup by Argentina in dramatic fashion, and were determined not to let lightning strike twice.
The majority of the massed ranks at the Adelaide Oval were swathed in green, but despite that support and being fired by memories of 1999, Ireland were strangely subdued in the opening exchanges when the Pumas took a deserved lead from the boot of Gonzalo Quesada.
At times of greatest need it is often left to the talismanic Keith Wood or Brian O'Driscoll to change Irish fortune with a bit of magic.
O'Driscoll has been out of sorts down under and it was Wood who finally gave the Irish hoardes something to cheer.
The skipper pounced on a loose Argentine line-out tap back, burst through the midfield and off-loaded to Quinlan, who dislocated his shoulder in going over.
Humphreys added the conversion and a penalty soon after, but just as the men in green looked to be finding their feet, Argentina came back.
Ireland gifted three points to their opponents with a poor re-start that gave Quesada the chance to land an ugly drop goal, despite a fumble in receiving the ball.
Another penalty saw Argentina turnaround one point adrift, and, playing the better rugby, they looked the more likely victors.
With his side struggling, Irish coach Eddie O'Sullivan threw on O'Gara midway through the second half, a plan that looked to have immediately back-fired.
The number 10 missed touch and Ignacio Corleto made him pay the price, landing a mammoth drop goal.
But O'Gara proved his worth with two crucial penalties.
In a nervy finish Argentina again closed to within one point, but Ireland held on to send their sizeable Adelaide support away in delight, and Argentina home.
Ireland are likely to face France in the last eight, unless they can pull off an even more memorable win over Australia next weekend.
Argentina: I Corleto; J Piossek, J Orengo, F Contepomi, D Albanese; G Quesada, A Pichot (capt); R Grau, F Mendez, M Reggiardo, I Lobbe, R Alvarez, L Ostiglia, R Martin, G Longo.
Replacements: M Ledesma, M Scelzco, P Albacete, S Phelan, N Fernandez Miranda, M Gaitain, Juan M Hernandez.
Ireland: G Dempsey; S Horgan, B O'Driscoll, K Maggs, D Hickie; D Humphreys, P Stringer; R Corrigan, K Wood, J Hayes (capt), M O'Kelly, P O'Connell, S Easterby, A Quinlan, V Costello.
Replacements: S Byrne, M Horan, D O'Callaghan, E Miller, G Easterby, R O'Gara, J Kelly.