The poll from Instituto DataFolha shows president Lula’s former cabinet chief and his personal choice to succeed him with 50% vote intention, while Serra from the Brazilian Social Democracy party figures with 27% and the candidate from the Green Party, Senator and former Environment Minister Marina Silva, counts on 11%.
Compared to a week ago Ms Rousseff retains her 50% plus vote intention, which ensures victory in the first October 3 round, avoiding a run off at the end of that month, on October 31st.
Serra who has a majority support among the business sector dropped from 28% to 27%.
Silva who broke off with Lula on environmental policies differences gained one point from 10% to 11%.
In the event of a run-off Ms Rousseff would garner 55% of the vote and Serra 35%, one point less than a week ago.
The poll was done September 8/9, with 11.660 interviews in 414 municipalities with a margin of error of plus or minus two percentage points.
The last weeks of the campaign have been engulfed by claims that followers of Ms Rousseff have been looking into – and selectively leaking to the press – bank accounts and fiscal reports of Serra family members and other opposition officials.