Challenger surges in Brazil's presidential race

A surging Marina Silva has narrowed President Dilma Rousseff's lead in Brazil's presidential race, a new opinion poll showed on Tuesday.

With the narrowing gap, a second-round runoff appears likely, and the popular environmentalist could be in a good position to win.

Silva, who was thrust into the presidential race last week following the death of her party's candidate, had the support of 29 percent of voters heading into the Oct 5 vote, according to the survey conducted by polling institute Ibope.

The poll showed Rousseff with 34 percent, down from 38 percent in the previous Ibope survey in early August. The other main opposition candidate, Senator Aecio Neves, has also dropped 4 percentage points to 19 percent since the last poll.

In a second-round runoff on Oct 26 between the top two vote-getters, Silva would defeat Rousseff by a margin of 9 percentage points, according to the poll, which has a margin of error of plus or minus 2 percentage points.

The election could decide whether the commodities powerhouse takes a more market-friendly direction that attracts the outside investment that's believed to be needed to revive the world's seventh-largest economy.

A renowned defender of the Amazon rain forest who placed a strong third in the 2010 presidential election, Silva has shaken up this year's race since declaring her candidacy last Wednesday. However, many political analysts warn that both Rousseff and Neves have plenty of television ad time, along with more powerful and better-funded parties behind them, to counter Silva's rise before election day.

Silva surged 10 percentage points ahead of Neves, the centrist candidate favored by investors, and now threatens to dislodge the ruling Workers' Party in its toughest election since it won office in 2002, the Ibope poll showed.

"Silva is the favorite for the runoff, where she will draw more of Neves' supporters than Rousseff," said Carlos Melo, a political scientist at the Insper business school.