Sao Paulo ? A former Marxist guerrilla chosen by Brazil’s beloved leader to succeed him will face a centrist rival in a presidential runoff after failing to get enough votes to win Sunday’s election outright, according to official results.

Dilma Rousseff, a 62-year-old career bureaucrat trying to become Brazil’s first female president on the ruling Workers Party ticket, captured 46.8 percent of the vote but needed 50 percent to win in the first round of balloting.

Former Sao Paulo state governor Jose Serra got 32.6 percent support, while Green Party candidate Marina Silva got a surprising 19.4 percent, likely spoiling the center-left Rousseff’s chance of a first-round win by siphoning off votes. The results came with 99.6 percent of the votes counted, according to Brazil’s Supreme Electoral Court.

The runoff election on Oct. 31 will pit Serra against Rousseff, who analysts say will be the heavy favorite, though a series of recent scandals could hurt the ruling party candidate.

“A second round is a whole new ball game. Everything starts from zero,” said Alexandre Barros, with the Early Warning political risk group in Brasilia. “I would say Dilma has a strong chance of winning a second round. But it will all depend on what new facts emerge during the campaign.”

Rousseff is the personal choice of outgoing President Luiz Inacio Lula da Silva, universally known as Lula, who led Brazil to unparalleled economic growth, increased the nation’s political clout on the global stage, and leaves office with 80 percent approval ratings, though he also needed second-round votes to win his elections in 2002 and 2006.

“We are used to challenges. Traditionally, we have fared well in the second round,” Rousseff told supporters in Brasilia. “I’m confident that the second round will provide an important process of elucidation, of dialogue with the representatives of society.”

Serra had yet to make a statement late Sunday.

Rousseff has left behind her radical rebel youth, been a pragmatic and results-oriented bureaucrat for years and has pledged to stick to the pragmatic market-friendly policy charted by Silva.