Incumbent president Dilma Rousseff and former Senator Marina Silva remain tied for support in a possible runoff vote, while third-place challenger Aécio Neves gained support for the first round vote, the latest poll from the Datafolha institute showed. The poll indicated Ms. Rousseff would win a first round with 37% of support, versus 30% for Ms. Silva and 17% for Mr. Neves. Support for Mr. Neves rose from 15% seen in a previous poll. Support for Ms. Rousseff rose from a previous 36% while support for Ms. Silva declined from 33%.  In a second round runoff vote, Ms. Silva would take 46% of the vote compared with 44% for Ms. Rousseff. Under Brazilian election rules, a runoff vote is held if no candidate takes 50% or more of valid votes in the first round. Brazilian voters are scheduled to participate in a first round vote on Oct. 5. The latest poll was taken among 5,300 voters on Sept. 18-19 and has a margin of error of 2 percentage points.