The Pumas sounded a warning to Pool B rival Scotland before their clash in Wellington this Sunday with a comfortable win against Romania in Invercargill on Saturday.
Scoring six tries to one, Argentina dominated up front and showed some of its sizzling attacking ability that had been stifled in the opening game against England.
Off the field, it is unlikely any of the 19 visiting teams is getting as much support.
Rugby Park is normally a sea of Stags maroon, but on Saturday the majority of the 12,600-strong crowd had donned Pumas blue and white, in a repeat of the first-round game at Otago Stadium.
The fans also sang boisterously in spells throughout the match, making for a wonderful atmosphere and delighting the players.
"We were amazingly surprised and really touched to see all those people here coming to see us," veteran hooker Mario Ledesma said.
"I said to the guys, 'You should enjoy that, enjoy this support, because I don't think that you will ever see that many Argentines united in the southern city of New Zealand'."
Lock Patricio Albacete echoed his team-mate's thoughts.
"It's incredible. We are very happy that they did such a journey to support us, despite the weather conditions. It's a real pleasure for us to play with them backing us."
Argentina will start as the favourite against Scotland, which has laboured to two unimpressive wins against Georgia and Romania.
Ledesma said the Pumas were not getting carried away with their performance against Romania.
"What we really wanted first was to win the game. And next week [against Scotland], the most important will be to win. We played well the first 30 minutes but then we did some mistakes that we will have to get rid of before the match against Scotland."
Argentina set the tone early, taking the Romanian challenge head-on and rumbling a maul up field.
The Oaks would have hoped for parity in the tight encounters but the Pumas dominated the forward exchanges, securing quick ruck ball and setting a superb platform for their halfback Nicolas Vergallo.
The Pumas spread the ball wide at every opportunity and stretched Romania's defence enough for first five-eighth Santiago Fernandez to waltz through a gap to score the opening try.
Moments later, powerful flanker Juan Manuel Leguizamon broke an ineffectual tackle and stormed towards the line, crashing through the last defender and looking, if for only a brief moment, like Jonah Lomu.
Trailing 14-0, Romania answered back with a penalty in the 13th minute through Tiberius Dimofte, a brief respite from the one-way traffic.
Two more tries later, and trailing 26-3, Romania found its way to the line, attacking the right flank and then swinging it left, for winger Ionel Cazan to finish a good team try.
Argentina was well in control but, if anything, was guilty of trying to play a little too much rugby. Fine moves often finished with a eager pass and a handling error. A little more patience might have seen Argentina score another two or three tries.
Replacement right winger Juan Jose Imhoff popped up on the left to score in the 64th minute, and flanker Genaro Fessia scampered the best part of 50m to complete the try scoring action.
The scores -
ARGENTINA v ROMANIA
• Argentina 43
Santiago Fernandez, Juan Manuel Leguizamon, Juan Figallo, Lucas Gonzalez Amorosino, Juan Jose Imhoff, Genaro Fessia tries; Martin Rodriguez 5 con, pen
• Romania 8
Ionel Cazan try; Tiberius Dimofte pen
• Halftime: Argentina 26-8