The Pumas ended a 35-year losing streak in Australia with a 23-19 win over the Wallabies on Saturday, continuing their strong form under new coach Mario Ledesma.
Not since 1983, in the first test meeting between the two nations in Brisbane, had Argentina beaten the Wallabies in Australia.
But former Wallabies scrum coach Ledesma helped mastermind the drought-breaking result against his former head coach Michael Cheika. A long-range penalty from Emiliano Boffelli with three minutes to go sealed the victory.
Israel Folau missed a chance to win it for the Wallabies after the siren. Folau had an unmarked Bernard Foley to his right but chose not to pass the ball to him and instead gave up possession as he tried to score himself.
Australia spent most of the second half searching for the points that would have given them the lead after Dane Haylett-Petty's 54th-minute try reduced the margin to 20-19.
The Wallabies crossed for the 11th-minute opener after some strong openside play from Haylett-Petty and Reece Hodge to set up Will Genia.
Argentina responded quickly. Hauled down just short of the tryline, Jerónimo de la Fuente popped up a ball for Nicolás Sánchez to streak through and score in the 15th.
Four minutes later, Folau found himself in space and made the most of it, moving past four Argentine defenders with right steps before planting down in the left corner.
But the Wallabies couldn't find another try for the remainder of the half despite enjoying good field position.
Argentina split a home-and-away series against South Africa to start its campaign before a 46-24 loss to the All Blacks last weekend. The Wallabies beat South Africa 23-18 last Saturday for their first win of the tournament.
David Pocock, returning from a neck injury, captained the Wallabies after regular skipper Michael Hooper's late withdrawal with a hamstring injury.
"That's a tough one to take," Pocock said. "Credit to Argentina. They played a smart game and put the pressure on us, and every time we got down there they seemed to make a play and we coughed up the ball."
"Even there right at the end we had an opportunity to win it. It's just that last bit of composure. We missed a lot of opportunities."
The win ended a six-match Argentina losing streak against Australia.
"I think the line-out was good, the maul and the scrum was the difference," said Argentina captain Agustín Creevy.
Ledesma said belief within his team is sky-high, crediting their work ethic for the breakthrough.
Ledesma, a former forwards coach with the Wallabies who was poached by Super Rugby side the Jaguares at the end of the 2017 season before Argentina snapped him up, said he was proud of his players.
"Thirty-five years is a long time, but the most important thing is what the boys are doing day-to-day and week-to-week, how they're working, the effort they're putting in," he said. "They believe in themselves, that's the most important thing here. This is their reward for what they are doing."
Ledesma, himself a former hooker, shifted the scrum around against Australia after it was exposed by the All Blacks, bringing in prop Santiago Medrano for Garcia Botta and blindside flanker Pablo Matera in place of Tomás Lezana.
He also had Gonzalo Bertranou back at scrum-half, and their scrummaging and defence was a key factor in the win.
"Although we had some mistakes and sometimes gave the ball away, we did many things well too," he said.
"At the beginning, we failed a bit in the one-on-one tackles, but we fixed that and got things together. We were far from perfect, but I congratulate the guys for what they have done."