Argentina's Economy Minister Sergio Massa and anti-establishment outsider Javier Milei will face off in a runoff presidential poll, preliminary election results showed late Sunday.

Latin America's third-largest economy is creaking under triple-digit inflation after decades of recurrent fiscal crises marked by debt, financial mismanagement, and a volatile currency.

The charismatic Massa, representing the ruling center-left Peronist coalition, overcame expectations to come first with 36.6% of votes, with more than 97% of ballots counted, despite overseeing record annual inflation and poverty levels.

"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.

If elected, Massa promised to lead a government of national unity, a first for Argentina, and launched an appeal to "all those who share our democratic values."

"I am not going to fail you," he said.

The libertarian Milei, who brought a powered-up chainsaw to rallies vowing to slash public spending and dollarize the economy, scored 30% 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 Nov. 19 runoff election, with the winner to take office Dec. 10.