On Sunday, the centrist Peronist economy chief scored some 37% of the vote ahead of far-right libertarian Javier Milei who received 30%, a surprise reversal of pre-vote expectations giving him the momentum into a Nov. 19 run-off.

Massa's win underscores how he managed to successfully play up fears that Milei's radical proposals to fix a broken economy could make things worse for the millions who are heavily reliant on state subsidies, despite voter anger at the government.

In the week running up to the vote commuters were shown two ticket prices on trains and buses with a low "Massa price" or far higher prices under his rivals without subsidies. Local media reported similar though more informal campaigns in some hospitals, and the energy secretary warned the price of subsidized gas could double.

Massa also expanded income tax exemptions to all workers earlier this month, a popular move though at a significant cost to already depleted state funds and fiscal targets agreed with major creditor the International Monetary Fund (IMF).

Milei, meanwhile, has pledged to "chainsaw" the economic status quo and privatize many state entities, gaining a strong backing by voters fed up with years of economic mismanagement, but also spooking some people with his often violent rhetoric toward his critics.

"For me it was a matter of time before people realized that Milei's proposals made no sense," said Amparo Anzaldi, 20, a student in Buenos Aires. "It is not going to be easy to take away our education or public health."