BRASILIA (AFP) - Brazil's presidential race is rapidly shifting gears with a surge in support for environmentalist Marina Silva sending a threatened Dilma Rousseff, the incumbent, into attack mode.
With a month to go until the election, the ground has abruptly shifted under Ms Rousseff - who had been the overwhelming favourite to win - since the Aug 13 death of Socialist Party candidate Eduardo Campos in a plane crash.
Mr Campos' death catapulted his running mate, Silva, into the race and suddenly Rousseff is faced with a fresh contender. Opinion polls show Ms Silva would defeat Ms Rousseff in a run-off by 10 points.
The first round of the elections are on October 5, with a run-off likely on Oct 26.
On Monday night, in the contest's second televised debate, Ms Rousseff went for the jugular, calling into question Ms Silva's ability to pay for her myriad campaign promises.
If she can regain the initiative and win, Ms Rousseff could give the Workers Party (PT) a fourth straight poll triumph - she succeeded popular two-term president Luiz Inacio Lula da Silva in 2011.
Mr Lula on Tuesday offered Twitter backing for Ms Rousseff, opening a new account, @LulapeloBrasil (Lula for Brazil).
"On October 5, reason will prevail," Mr Lula predicted.
"If we want what is good for this country, for it to remain productive and generating jobs, then we must choose Dilma."
Ms Silva, born into a family of poor rubber tappers, served as environment minister for five years under Mr Lula.
Having last year failed to gain enough signatures to stand as the candidate of her "sustainability network", Ms Silva threw in her lot with the Socialist Party (PSB), and since taking the torch from Mr Campos has raced to parity in voter intentions.
"Today, Marina is making the news in the election and is very competitive. In two weeks, everything changed. A month hence, anything can happen," political analyst Andre Cesar of the Prospectiva consultancy told AFP.
Mr Cesar said a stung Ms Rousseff had changed tack in Monday's televised debate.
"She is going to go on the offensive... as that is the only way to defeat Silva - though it could boomerang," he noted, as Ms Rousseff's administration battles an economic recession her rivals largely blame on her government.
Ms Rousseff used the debate to ask Ms Silva how she would fund a raft of policies - the latter notably wants to invest 10 per cent of GDP in education and also boost health spending. In all, Ms Silva has unveiled a mammoth US$60 billion (S$75.2 billion) of policy commitments.
Whereas Ms Silva at the weekend rowed back on support for gay marriage - the evangelical Christian has since reiterated her backing for civil unions - Ms Rousseff on Monday underlined her unequivocal support for the former, while criminalising homophobic behaviour.
"Rousseff is going to look for areas where Marina could have problems," said Mr Cesar.
Those include "economic policy, her relations as an ecologist with agro business" - a powerful sector with which Ms Silva's running mate Beto Albuquerque has strong links.
Ms Silva, who stood for the Green Party in 2010 and came in third with a respectable 20 per cent vote share, was one of the few politicians not to see her image take a hit during the mass demonstrations of June last year.
An electorate demanding more investment in health, education and transport in particular is generally fed up with politicians and parties of all stripes.
Ms Silva is gaining ground in the south-east, where Sao Paulo and Rio are located and which were major centres of protest last year.
Ms Silva is "the alternative" many are willing to take a chance on, said Mr Cesar.
But Ms Rousseff retains support in the poorer north-east, which has gained from her party's social welfare programmes - also a major reason for Mr Lula's success.
"The most recent polls show the 'Marina phenomenon' is not just in reaction to the death of Campos but that she is here to stay," said US-born analyst David Fleischer of the University of Brasilia.
"If Marina keeps on gaining ground at Rousseff's expense, she could win in the first round."
But, analysts say, social democrat Aecio Neves could also have a say.
Mr Neves, trailing both women in third place, is taking a more conciliatory tack as he positions himself for a potential post-vote alliance.
"Neves will have to measure carefully his attacks on Marina given that he could be an ally to help her win the run-off," said Mr Fleischer.