The Olyroos scored a goal in each half, and in between Argentina saw midfielder Francisco Ortega sent off when he got his second yellow card for an innocuous collision just before half-time.

Referee Srdjan Jovanovic was also happy to hand out cards to the Aussies, with seven yellows being handed to players in green and gold.

It could be a problem going forward, but for now the Olyroos are happily on top of group C thanks to their win over the favoured Argentinians, and a 0-0 draw between Spain and Egypt.

Coach Graham Arnold declared before the game that his side would "shock the world" and they did just that.

"We are here to compete for a gold medal, we're not here to compete with the numbers," he said.

"I know in the past that it's seen just as a success to make the Olympics. I don't see that. We're here to compete for a medal like all the other teams."

Western United's Lachie Wales scored the opener in the 14th minute when he latched onto a Joel King cross at the far post and put his side-footed first touch past Argentine goalkeeper Jeremias Ledesma.

The Australians kept pressing and were applying the pressure in first-half stoppage time, when Argentina surprisingly lost one of their players for the rest of the night.

The teams were jostling for position in the box as the Olyroos lined up for a corner, prompting Jovanovic to warn both sides for getting a little too physical.

After he let them get back to playing, he immediately pulled things up again, pulling out a yellow card for Ortega, which was his second in a matter of moments and sent him for an early shower.

Replays showed he had lightly clashed with Riley McGree as the pair fought for a good position, but any card, let alone a send-off was harsh.

The Olyroos kept Argentina at arm's length for most of the second half before 19-year-old Marco Tilio sealed the win 30 seconds after coming onto the field in the 80th minute, sending a beautiful strike into the top corner from outside the 18-yard box to finish off a counter-attack that he himself started just on the wrong side of halfway.

Arnold said he hoped the result put smiles on the faces of Australians in lockdown back home.

"It was probably the last thing I mentioned before the boys went on the pitch," he said.

"Australia — New South Wales especially — is going through a tough time at the moment with COVID-19.

"I said to the boys there's a lot of families at home in lockdown, let's put a smile on a lot of Australian faces and give them something they will remember.

"There were probably a lot of people back home who didn't give us a chance of winning the game before but really enjoyed that tonight.

"Sometimes when you mention the name of a nation like Argentina everyone starts thinking of Diego Maradona, Lionel Messi and them being Copa America champions.

"But it was more about focusing on ourselves for the last week and making sure that all their players knew their roles and jobs. We had to have the belief that we could win the game."