“Our country is in a complicated situation … nevertheless you believed we were the best tool to build a new step in Argentina’s history,” Massa told his cheering supporters in Buenos Aires.

The libertarian Milei, who brought a powered-up chainsaw to rallies vowing to slash public spending and dollarise the economy, scored 30.51 per cent of the vote.

The rock-singing, TikTok-savvy outsider came from nowhere to put up a fierce challenge to traditional political parties, touching a nerve with Argentines fed-up with economic shambles.

“Today is a historic day because two-thirds voted for change. All of us who want change have to work together. We can win, take back our country, prevent our kids from leaving the country,” said Milei.

The two will compete in a November 19 run-off election, with the winner to take office December 10.

In his victory speech Massa sought to present himself as the calmer, steadier hand, as opposed to Milei, who surged to prominence with his angry diatribes against the “thieving and useless political class” and dire state of the country’s economy.

“I am convinced that this is not a shit country. It is a great country and we are going to give it the place that it deserves,” said Massa.

During the campaign, Massa took pains to highlight what his opposition’s plans to cut hefty electricity and public transport subsidies would mean for people’s pockets.

To woo voters, he went on a pre-election spending spree, slashing income tax for much of the population in a move analysts said would only make the country’s fragile financial situation worse.

Milei, a libertarian economist, blindsided pollsters when he surged to the front of the election race, winning an August primary with 30 per cent of votes.

However, he kept the same amount of votes in the first-round election.

While some are keen for a radical shift, “a lot of Argentines have a lot to lose from the dismantling of the social welfare state,” which supports millions, said Benjamin Gedan, director of the Argentina Project at the Washington-based Wilson Centre.

“If Milei is at rallies wielding a chainsaw, well, at the other end of that chainsaw is people’s quality of life.”

However, with over eight million votes up for grabs that went to third-placed former security minister Patricia Bullrich and two other candidates, he said Massa faces a stiff battle against the upstart Milei.

“I think a simple reading of this first-round result is that many more Argentines want to throw Peronists out of power than the number who would like to see them remain,” said Gedan.

Analysts say Milei’s surge follows the regional trend towards anti-establishment parties, and he is often compared to former US president Donald Trump or Brazil’s Jair Bolsonaro.

Bolsonaro’s son Eduardo was present in his election bunker Sunday to show his support.

“I believe that Milei will win, whether it’s in the first or second round doesn’t matter,” he said.

Milei, a self-described “anarcho-capitalist,” is against abortion and sex education, wants to ditch about 10 government ministries, and does not believe humans are responsible for climate change.

With 40 per cent of the population living in poverty and a middle class brought to its knees, many voters are drawn to Milei, seeing traditional parties as the architects of their misery.

Many casting their ballots were jittery over the impact of the vote on the volatile peso and inflation, and said they were simply choosing the least worst option.

“There is so much uncertainty … and fear, out of these candidates, there are none who represent me. There is no one who can change what we need here in Argentina,” said graphic designer Maria Olguin, 40.

Additional reporting by Bloomberg