The poll published on Friday was conducted by Sensus, a research institute that is not as closely watched as Brazil's larger polling firms Ibope and Datafolha, whose polls show Neves and Rousseff in a dead heat.
If the runoff were held today, Neves would win 56.4 percent of the valid votes - which exclude undecided voters, spoiled and blank survey responses - against 43.6 percent for Rousseff, Sensus said.
The previous Sensus poll last week had given Neves an even larger margin of victory of 17.6 percentage points.
Neves, the financial markets' favorite, gained ground after his stronger-than-expected showing in the first-round vote on Oct. 5, when he bested environmentalist Marina Silva to place second behind Rousseff. But the latest Datafolha and Ibope polls show his support has stopped growing, Reuters reported.
Sensus interviewed 2,000 voters between Tuesday and Friday. Its results were posted on the website of weekly news magazine IstoÉ.