By Nicolás Misculin

BUENOS AIRES Argentina's Peronist Economy Minister Sergio Massa may be about to pull off a political miracle: win a presidential election despite being at the helm of the country's worst economic crisis in decades and with inflation nearing 150%.

The 51-year-old political wheeler-dealer pulled off an unexpected first place in the South American country's first-round vote in October and is neck-and-neck with libertarian rival Javier Milei ahead of Sunday's run-off, something unthinkable just months ago when the government looked dead and buried.

The lawyer, a moderate who is seeking to revive and reshape the Peronists from the ashes of crisis, has been on an all-out charm offensive, luring voters with tax cuts and reaching out across the political aisle, pledging a unity government.

"He is a tireless worker, in dialogue with everyone," said Malena Galmarini, president of state water utility AySA, a Peronist activist and Massa's wife.

"He knows the state like few others and that is why he is the most qualified to govern a new stage for Argentina."

Massa does, however, have major baggage. Some 40% of the population is in poverty, a $44 billion program with the International Monetary Fund (IMF) is on the rocks and a recession is looming.

Economy minister since last year, Massa has also been unable to tame inflation - now at its highest since 1991, and still rising - but has played up the Peronists' track record of protecting welfare payments and subsidies that keep utilities and transport costs low, while warning prices could jump further under Milei.

That tactic helped him come top in the October first round by almost seven points, beating pollster predictions, and could help him again on Sunday despite Milei winning the support of some key conservative backers.

Graciela Roldan, 40, an administrative employee in Buenos Aires, said that she would vote for Massa and that he offered protection from "an evil being that is threatening our rights".

"If he manages to position himself as a defender of the people and the middle class, as he has been doing with his latest measures, he can be a icon and Peronist leader in the search for social equality," she said.

POLITICAL CHAMELEON?

Massa's biggest win so far has been to unite a Peronist coalition that was on the verge of falling apart, as supporters of moderate President Alberto Fernandez fought with the leftist wing around powerful Vice President Cristina Fernandez de Kirchner.

He got the backing of the full coalition, but has distanced himself from unpopular Fernandez and divisive former two-term leader Kirchner, pledging something new to angry voters.

"Massa is the least Peronist of the Peronists," said analyst Julio Burdman from the Electoral Observatory, adding his "malleability" was his biggest strength to win moderate votes.

Massa's critics contend he is a "pancake" - easily flipped.

A career politician, Massa was chief of staff in the first Kirchner term, but then clashed with her and left to set up his own political party. He later returned to Peronism, although his back-and-forth has led some in the movement to distrust him.

Argentine Foreign Minister Santiago Cafiero told Reuters Massa would establish his own style of leadership if elected, and for now had unified the coalition to face the election.

ECONOMY ON VERGE OF COLLAPSE

The son of Italian immigrants, Massa studied at a Catholic school in the suburbs of Buenos Aires, where he became active in Peronism after spending time in a conservative political party.

He was elected as a provincial deputy when he was only 27 years old, before going onto roles including as mayor of Tigre, an important suburb north of Buenos Aires.

Those who know him highlight his ability to achieve consensus.

"He is a person who works a lot on the relationships. He doesn't just talk to his own people, but also to those who think differently, he talks to practically the entire opposition," said an adviser who has worked with him for decades and asked to remain anonymous.

Agustin Rossi, running for vice president on Massa's ticket, previously told Reuters Massa had shown guts by taking on the economy role and "steering the ship" at a very tough time. "In Peronism, that is highly valued, not running away from difficulties," he said.

The economic malaise, nonetheless, could hurt him at the polls - and afterwards, if he were to triumph.

"The economy is on the verge of collapse," said Benjamin Gedan, director of the Wilson Center's Latin America Program. "Massa's charm is no match for hyperinflation."

(Reporting by Nicolás Misculin; Editing by Adam Jourdan and Rosalba O'Brien)