Leftist incumbent Dilma Rousseff is the narrow favourite heading into the vote, with a four- to six-point advantage over center-right business favourite Aecio Neves in the race to lead the world's seventh-largest economy, Saturday's final surveys showed.

Datafolha gave Rousseff a 52-48 per cent lead, just on the two-percentage-point margin for error, while indicating it saw a "probability" of her winning the contest.

An Ibope Institute poll for its part showed Rousseff ahead by 53-47 per cent, breaking the technical tie.

Winning back front-runner status has been a battle for Brazil's first woman president - a former guerrilla once jailed and tortured for fighting the country's 1964-1985 military regime.

The vote is widely seen as a referendum on 12 years of government by her Workers' Party (PT) - eight under working-class hero Luiz Inacio Lula da Silva and four under Rousseff, his seemingly less-charmed successor.

The party endeared itself to the masses with landmark social programs that have lifted millions from poverty, increased wages and brought unemployment to a record-low 4.9 per cent.

But after Brazil benefited from an economic boom during the Lula years, the outlook has darkened since Rousseff won the 2010 election, the year economic growth peaked at 7.5 per cent.

Rousseff, 66, has presided over rising inflation and a recession this year. She has also had to deal with massive protests last year against corruption, record spending on the World Cup, and poor services, notably education, health care and transport.

She has also been battered by a multi-billion-dollar embezzlement scandal implicating dozens of politicians - mainly her allies -- at state-owned oil giant Petrobras.

Before the October 5 first-round vote, she had to fend off environmentalist Marina Silva, who surged in the preference polls with her vow to become Brazil's first "poor, black" president when she dramatically entered the race after running mate Eduardo Campos died in a plane crash.

No sooner had the PT electoral machine dispatched Silva - who exited the first round with 21 per cent of the vote, to Rousseff's 42 per cent and Neves's 34 per cent - than the incumbent had to beat back Neves, who converted the momentum of his first-round comeback into a narrow lead.

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