Argentina bounced back from their opening defeat by England to secure a six-try bonus-point win over Romania.
The confident Argentines had the extra point secured in the opening 30 minutes following four tries in an impressive first-half performance.
Romania had given Scotland a scare in their opening group game last weekend, eventually losing 34-24.
But they had no answer to the Pumas' attacking verve, though Ionel Cazan did cross the whitewash in the 31st minute.
The impressive Argentines combined dynamic forward play with backline adventure.
Only four minutes had gone when outside-half Santiago Fernandez crossed under the posts for his first international try and Argentina were soon comfortably leading through tries from Juan Manuel Leguizamon, Juan Figallo and Lucas Gonzalez Amorosino.
Martin Rodriguez converted three of the tries to take the score to 26-3.
Romania's only points up to that point had been from a Tiberius Dimofte penalty, but they scored their only try after 31 minutes in what was a rare foray into opposition territory, spinning the ball wide to the left for Cazan to dive over in the corner.
The Romanians were dogged, even when reduced to 14 men when Mihaita Lazar was sent to the sin bin at the start of the second half, but an upset was never on the cards, especially when Juan Jose Imhoff sauntered through an absent defence to extend the lead to 36-8 in the 63rd minute.
Argentina got a sixth try through replacement Genaro Fessia and the result will no doubt give forthcoming opponents Scotland plenty to ponder ahead of what could be a decisive Pool B match in Wellington on 25 September.
"We were desperate to get a win, that was the only option for us," said Argentina captain Juan Martin Fernandez Lobbe.
"The idea was to have a win and get a bit of confidence, and we got a lot of confidence from that match."
Argentina: Gonzalez Amorosino, Camacho, Bosch, Rodriguez, Agulla, Fernandez, Vergallo, Roncero, Ledesma, Figallo, Carizza, Albacete, Campos, Leguizamon, Fernandez Lobbe.
Replacements: Jose Imhoff for Camacho (50), Sanchez for Fernandez (76), Lalanne for Vergallo (69), Scelzo for Roncero (58), Creevy for Ledesma (40), Galarza for Campos (74), Fessia for Leguizamon (57).
Romania: Dumitras, Lemnaru, Gal, Gheara, Cazan, Dimofte, Surugiu, Lazar, Tincu, Ion, Ursache, Petre, Macovei, Tonita, Carpo.
Replacements: Vlaicu for Dumitras (48), Calafeteanu for Surugiu (69), Popirlan for Petre (48), Ianus for Macovei (76), Florea for Carpo (54). Not Used: Zebega, Dumbrava.
Sin Bin: Lazar (54).