Australia claimed their first major scalp under coach Joe Schmidt, defying rain and a raucous home crowd to upset World Cup semi-finalists Argentina 20-19 with a penalty goal after the siren that secured a stirring comeback win in La Plata and keeps their Rugby Championship hopes alive.

After back-to-back shellackings by South Africa, the Wallabies went into this Test as 3-1 outsiders; Los Pumas have claimed their past two encounters and were fresh from last month’s epic defeat of the All Blacks. But in slippery conditions, the men in gold overcame a litany of errors and found a way to peg back a 10-point deficit and squeak home with a last-gasp kick to grind out the win.

With 39-year-old hooker Agustín Creevy playing the final Test of a 19-year career, emotions ran high as tears and rain trickled down the faces of Los Pumas during the anthems. To diffuse so impassioned a foe, Australia needed composure and precision but could initially summon neither. Lukhan Salakaia-Loto dropped his first pass from the kick-off and Tom Wright sliced his first kick. Flyhalf Noah Lolesio was mixing up his attack but for all the variety, the result was the same: turnover ball to Los Pumas.

Even in attack, Australia went backwards. At one stage in the opening minutes they went 27 phases, back and forth, left and right, without ever denting the Argentina 22, then losing 70m in a flash when a Hamish Stewart grubber allowed Juan Cruz Mallia to reef it downfield and set up Santiago Carreras’s 12th minute penalty goal for 3-0.

In the 16th minute another bung boot set up Argentina’s maul to roll over for 10-0. Soft errors from the Wallabies and sharp hands from Los Pumas were lifting the home crowd. It took time and patience but Australia found a response in the 27th minute when Rob Valetini bent the line and a flurry of inside balls finally gave Len Ikitau the chance to loop a low pass to Jake Gordon who crossed under the posts for 10-7.

It was the Wallabies’ second try in 187 minutes of play in the Rugby Championship. But celebrations soured when Stewart illegally entered a ruck and Carreras extended Argentina’s lead to six points. A smart turnover from Angus Bell rescued Australia in their red zone and forced an error at the other end. But Lolesio missed the kick from 37m out to send the sodden teams to the half-time break with the scoreboard at 13-7.

With 57% of possession but precious little territory to show for it, Schmidt’s first away game after five Tests as national coach was going to the wire. The rain stopped in the second half but not Australia’s mistakes, fumbling the restart. But despite some thumping tackles from captain Harry Wilson and Ikitau to win back possession, a dubious 45th-minute scrum penalty gifted Carreras another penalty goal for 16-7.

A Bell bellringer jolted Australia back into the contest. The prop prodigy, back from foot surgery, smashed his runner, won a turnover and set up a surge to the line. The Wallabies botched that chance when Gordon and Wilson attacked the two metre blindside, not the acreage out wide. But the men in gold came again down the left edge and then through the middle to allow No 8 Valetini to power over to bring the margin down to two points.

Now Australia had the momentum, they went with it. Young flanker Carlo Tizzano was tackling like a dervish and Ikitau was consistently breaking the line to give Lolesio time and create wave after wave of attack. The pressure told and, pinned in their quarter, Argentina erred again to let Lolesio kick Australia into the lead by 17-16.

After a desperate hour, both teams brought on reinforcements. The fresh legs lifted the home side and only Jake Gordon’s last-ditch tackle stopped Thomas Gallo from scoring when he was over the line. As heavy rain resumed, Argentina took back the lead, converting pressure into points to make it 19-17 entering the final 10 minutes. And to deliver the knockout Los Pumas brought on their hometown hero Creevy.

But it was the Wallabies who almost delivered the coup de grace, Lolesio finding the gap and racing down the outside looking for his 19-year old speedster Max Jorgensen. But again they fumbled the chance, the pass sailing too high to grab. But the visitors refused to drop their heads and set up camp, grinding and finding space, finally cracking the blue wall to allow replacement pivot Donaldson to kick them to victory after the final siren.