Argentina became the first team to beat Six Nations grand slam winners Wales at home this year as they recorded a come from behind 26-12 win over the Welsh at the Millennium Stadium.
Second-half tries by Juan Imhoff and Gonzalo Camacho proved the difference as the Pumas' recorded only their second win in Wales - their previous being 11 years to the day of their latest exploit.
Following their involvement in the Rugby Championship there were fears in Wales that the South Americans could catch the grand slam champions cold.
And they took full advantage with a pair of scintillating tries from their wings to bring Wales crashing down to earth and end any hopes of them climbing to fourth in the world rankings which would have seen them be seeded top of a 2015 World Cup pool.
Wales were without several of their grand slam stars with Adam Jones, Dan Lydiate, Ryan Jones and Jonathan Davies all ruled out through injury.
Aaron Jarvis slotted into the front row to make his debut while Tavis Knoyle was preferred to Mike Phillips at scrum-half.
Jamie Roberts, who will leave Cardiff Blues at the end of the season, lined up at inside centre opposite Felipe Contepomi, who inspired the Pumas to victory in 2001.
The veteran play-maker sat out the recent Rugby Championship but was recalled for the autumn series and opened the scoring on three minutes after Ian Evans was penalised for a high tackle.
Wales quickly hit-back through Halfpenny, after Jarvis settled any early nerves with a penalty earned at the scrum, but Argentina regained their lead thanks to a Nicolas Sanchez drop-goal.
But Argentina were dealt a major blow on 13 minutes when they lost Contepomi to a knee ligament injury and moments later Halfpenny knocked over his second penalty.
Wales lost their own inside centre midway through the opening half as Roberts suffered a heavy bang to the head but Halfpenny fired the hosts into the lead with his third successful shot at goal.
Sanchez struck the uprights within minutes of the restart and totally miscued a second attempt minutes later as he slipped over on the greasy Millennium Stadium turf.
And Halfpenny punished the Pumas for their inaccuracy as he maintained his 100 per cent strike rate with another penalty but Sanchez made some amends with a second opportunist drop-goal.
The Pumas continued their resurgence and sparked the game into life with the opening try.