Brazil's Rousseff extends lead over Silva in election poll

BRASILIA (Reuters) - President Dilma Rousseff is leading her closest rival Marina Silva by nine percentage points for a likely second-round runoff to Brazil's presidential election, a new opinion poll showed on Monday.

Rousseff would win the runoff with 47.7 percent of the votes against 38.7 percent for Silva, widening her lead from the one-point advantage she had in the previous survey by polling firm MDA last week.

The first round of Brazil's presidential election is on Sunday. If no candidate wins more than 50 percent of the valid votes, the election will be decided on Oct. 26 in a runoff between the top two vote-getters.

The election is being closely watched by investors who would like to see Silva, a popular environmentalist who has embraced pro-market policies, unseat leftist Rousseff and end 12 years of Workers' Party rule.

In a first round vote, Rousseff would take 40.4 percent of the votes and environmentalist Silva 25.2 percent, the MDA poll showed. That compares with 36 percent for Rousseff and 27 percent for Silva in the previous MDA poll. Support for centrist candidate Aecio Neves, the market favourite stuck in third place, has risen to 19.8 percent from 17.6 percent last week.

MDA polls are not as closely watched by political analysts as the surveys by bigger research firms Datafolha and Ibope, which use larger samples of voters and conduct polls more frequently.

Silva, who was thrust into the race when her party's original candidate was killed in a plane crash last month, initially surged on the support of voters who back her pledge to clean up Brazilian politics. But criticism of her ability to govern without Brazil's traditional parties from the Rousseff and Neves campaigns has eroded her support.

The MDA poll showed that Silva's rejection rate, or those who say they would never vote for her, has risen to 42.5 percent from 29.3 percent in late August, while Rousseff's rejection numbers have fallen four points to 41 percent.

The Rousseff government's approval rating, meanwhile, has climbed steadily to 41 percent from 33.1 in late August, according to MDA. The poll also showed that 61 percent of voters think that Rousseff will win the election.

Investors blame Rousseff's policies for the stagnation of Latin America's largest economy and the poll numbers showing the president consolidating her re-election chances weighed on markets.

The Brazilian real retreated to its weakest level in nearly six years on Monday and the benchmark Bovespa stock index fell 4.52 percent, its biggest one-day drop in over three years.

The MDA poll, which was commissioned by the transport industry lobby CNT, surveyed 2,002 people on Sept. 27-28. It has a margin of error of plus or minus 2.2 percentage points.

(Editing by Meredith Mazzilli and Marguerita Choy)