Rio de Janeiro, October 3 (Mercopress-RHC) -- Brazilian President Dilma Rousseff has extended her lead over environmentalist Marina Silva ahead of Sunday's presidential election and would win a likely second-round runoff, a new poll showed on Thursday.

Rousseff has 43% of voter support compared to 36% for Silva, according to the survey by the Ibope poll, widening her advantage to seven percentage points from four since the previous poll released on Tuesday.

In first-round voting that takes place on Sunday, Rousseff has 40% voter support and Silva 24%. That compares with 39% for Rousseff and 25% for Silva in the previous Ibope poll. Support for centrist candidate Aecio Neves was unchanged at 19%.

If no candidate wins an outright majority in the first round, the election will be decided in a runoff between the two leading candidates on October 26th.

The new Ibope poll surveyed 3,010 respondents nationwide between September 27th and October 2nd. The survey has a margin of error of plus or minus two percentage points.