Brazilian opposition presidential challenger Marina Silva would tie incumbent president Dilma Rousseff in a a first round vote and win by at least 10 percentage points in a runoff, according to a poll released Friday by the Datafolha opinion research institute. The poll showed the two candidates with support from 34% of respondents in a first round vote, while third place candidate Aecio Neves obtained support from 15%. In a runoff vote, Ms. Silva would obtain support from 50% of voters, compared with 40% for Ms. Rousseff. Ms. Rousseff, however, would defeat Mr. Neves in a runoff by a margin of 48% to 40%. According to Brazilian election rules, a runoff election is held if no candidate gets more than 50% of the vote in the first round. Ms. Silva, of the Brazilian Socialist Party, recently received the nomination from her party after the party’s initial candidate for the post, former Pernambuco governor Eduardo Campos, died earlier this month in a plane crash. The latest poll, sponsored by the Folha de S. Paulo newspaper, was taken among 2,874 voters on Aug. 28-29 and has a margin of error of 2 percentage points. Brazil is scheduled to hold a first round of nationwide general elections on Oct. 5.