By Anthony Boadle
BRASILIA (Reuters) - Environmentalist Marina Silva has widened her lead over President Dilma Rousseff to 10 percentage points in what could be a likely runoff in Brazil's October election, a survey by polling firm Datafolha showed on Friday.
It was the third poll in less than a week that projected the Oct. 5 election would go to a second-round vote in which Rousseff would be unseated by Silva, who entered the race just 10 days ago following the death of her party's candidate.
The popular anti-establishment figure is threatening to end the 12-year rule of the Workers' Party in a hotly contested vote that is being watched closely by investors hoping that a change of government will issue in more market-friendly policies.
Silva has surged to 34 percent support from 21 percent in a previous Datafolha poll conducted before she launched her candidacy. She is now tied with Rousseff whose support has fallen to 34 percent from 36 percent in a first-round vote.
If the race goes to a runoff on Oct. 26 as expected, Silva would win 50 percent of the votes, while Rousseff would get 40 percent, widening her margin of victory from six to 10 percentage points, according to Datafolha.
Support for centrist candidate and market favorite Aecio Neves has dropped to 15 percent from 20 percent in the previous poll on Aug. 18.
With Rousseff's re-election chances looking dimmer in the polls, the president suffered another blow on Friday with the publication of data confirming Brazil has fallen into recession.
The recession will give her opponents a powerful weapon at a moment when her candidacy is at its most vulnerable just five weeks from election day.
Neves lambasted Rousseff's "failed" policies for leading Brazil into recession, while Silva vowed to restore credibility of the country's economic management to draw back investors and return the once-booming economy to a path of prosperity.
Silva appeals to voters disenchanted with Brazil's political establishment who see her as a principled outsider who can govern ethically. Polls showed her drawing disenfranchised and uncommitted voters, and stealing support from Neves.
To stay in the race, Neves has had to step up his attacks on Silva, targeting her lack of executive experience and her plan to renew Brazilian politics by eschewing alliances with the traditional parties, which he has called illusory.
"I offer Brazil a concrete possibility of transforming our dreams into a better reality," the former governor and scion of a political family said at a campaign stop on Thursday.
The poll of 2,844 eligible voters was conducted Aug. 28-29 and has a margin of error of plus or minus two percentage points. The results were broadcast on TV Globo and posted on the website of the Folha de S.Paulo newspaper.
(Reporting by Anthony Boadle and Alonso Soto; Editing by Ken Wills)