This came after the Peronist opposition threw a curve-ball as the widely popular but corruption-tainted former president Cristina Kirchner surprisingly opted to run as vice president on Fernandez's ticket.
Kirchner elicits as much abhorrence as admiration, but Fernandez is a moderate who can appeal to a wider range of the Peronist electorate.
And he's no yes-man: although he was once Kirchner's cabinet chief, he subsequently became one of her fiercest critics before they buried the hatchet.
Sunday's result came as a shock for Macri, not because he lost but because of the margin of defeat.
Fernandez's 47 percent share is enough to win the October 27 election outright and avoid a run-off.
It might be scant consolation, but Macri does at least stand to become the first non-Peronist since 1928 to complete a presidential term.
Beyond left and right
Peron spent 18 years in exile following a military coup, but when he returned to his country in 1973, he declared that all Argentines were Peronists.
While that may not be true, the continued success of Peronists shows that the movement's cross-ideological allure endures, even if the political movement's ability to incorporate such a broad range of traditionally opposing ideas is less clear.
When it comes to Peronism, experts say, the traditional definitions of left and right serve no purpose.
Historian Gustavo Nicolas Contreras explains that the movement's three main principles – political sovereignty, economic independence and social justice – are sufficiently broad that sectors of society as diverse as blue-collar workers, industrial bourgeoisie and the most nationalist elements of the army can all identify with them.
Such ideological acrobatics are very much in line with Peron's own thinking, said political analyst Rosendo Fraga.
"Peron could oscillate from left to right without losing his political objective, which was to reach, retain or regain power," he said.
This far-ranging reach has allowed Peronism to survive dictatorships, the death of its founder, election defeats and even the armed conflict between the extreme left and right during the 1970s.
Contreras sees the existence of such distinctive ideologies under the same umbrella as Peronism's strength.
"Peronism is a political opportunity. It has the political weight that government can offer the possibility to strengthen your own interests," said Contreras.
The key to that strength is "its capacity to understand, process and represent the complexity, ambiguity and contradiction of Argentine society," said Fraga.
That's why, in the 1990s, Peronist president Carlos Menem managed to implement policies that favored the free market.
He privatized state companies in response to demands for change after the hyperinflation and decline of public enterprises during the centrist social-liberal Raul Alfonsin's administration, Fraga explained.
Menem's political model failed at the start of the 21st century, but that wasn't the end for Peronism.
"People started asking for more state (intervention) and internationally it wasn't so clear that the market economy was the only alternative," said Fraga.
Nestor Kirchner was also a Peronist but during his presidency from 2003 to 2007 he "interpreted this change and turned towards the center-left," and adopted an "interventionist model and populist direction," Fraga said.