(Corrects headline to say Rousseff holding lead against Silva (not Rousseff) surge)
BRASILIA, Aug 27 (Reuters) - Environmentalist Marina Silva has narrowed President Dilma Rousseff's lead down to six percentage points in Brazil's presidential election race and would defeat her in a likely second-round runoff, a new opinion poll showed on Wednesday.
Silva, who launched her bid last week following the death of the party's candidate, has 28.2 percent of voter support heading into the Oct. 5 vote, according to the survey by polling firm MDA.
The poll showed Rousseff with 34.2 percent, down from 36.2 percent in the previous MDA survey in early August. The other main opposition candidate, Aecio Neves, has 16 percent support, down from 22.1 percent in the last MDA poll.
If the race goes to a second-round runoff on Oct. 26 between the top two vote-getters, Silva would defeat Rousseff by a margin of six percentage points, the poll showed.
The MDA poll commissioned by the transport industry lobby CNT surveyed 2,002 people between Aug. 21-24 and has a margin of error of plus or minus 2.2 percentage points. (Reporting by Anthony Boadle; Editing by Jeffrey Benkoe)