Rousseff held a slight lead in one major poll over her center-right opponent, Aecio Neves, but the two were deadlocked in another.
The choice between Rousseff and Neves has split Brazilians into two camps those who think only the president will continue to protect the poor and advance social inclusion versus those who are certain that only the contender's market-friendly economic policies can see Brazil return to solid growth.
"Brazilians want it all. They are worried about the economy being sluggish and stagnant but they want to preserve social gains that have been made," said Michael Shifter, president of the Washington-based Inter-American Dialogue. "The question is which candidate is best equipped to deliver both of those."
Neves has hammered at Rousseff over a widening kickback scandal at state-run oil company Petrobras, with an informant telling investigators that the Workers' Party directly benefited from the scheme.
Rousseff has rejected those allegations and told Brazilians that a vote for Neves would be support for returning Brazil to times of intense economic turbulence, hyperinflation and high unemployment, which the nation encountered when the Social Democrats last held power. "We've worked so hard to better the lives of the people, and we won't let anything in this world, not even in this crisis nor all the pessimism, take away what they've conquered," Rousseff said before voting in southern Brazil.