Brazil's leftist President Dilma Rousseff won a first-round election on Sunday and will face business favorite Aecio Neves in what is shaping up to be a hard-fought runoff.

With nearly all ballots counted, Rousseff had 41 percent of the vote and Neves 34 percent, leaving popular environmentalist Marina Silva - who once looked set to become Brazil's first black president - relegated to third place with 21 percent.

Rousseff, the incumbent who is looking to win a second four-year term and extend 12 years of Workers' Party government, is the current favorite three weeks from the runoff vote, which is scheduled for Oct 26.