Brazilian opposition leader Jose Serra must lure environmentalists and others who backed a third-party candidate in yesterday's election if he is to derail frontrunner Dilma Rousseff's march to the presidency.
Mr Serra's underdog candidacy remained alive after Ms Rousseff, a former Marxist guerrilla handpicked by President Luiz Inacio Lula da Silva to succeed him at the helm of Latin America's largest economy, fell short of the 50 per cent of votes needed for outright victory.
With nearly all the ballots counted, Ms Rousseff had won 46.9 per cent to Mr Serra's 32.6 per cent. They will face each other in an October 31 runoff.
Opinion polls had shown Ms Rousseff on track to win a first-round victory, but a corruption scandal and some voters' unease about her views on social issues appeared to cost her support while boosting the Green Party's Marina Silva.
Ms Silva, an evangelical Christian and former environment minister, was the surprise of yesterday's vote, grabbing 19.3 per cent. Opinion polls had put her support at about 15 per cent.
At late-night rallies, Ms Rousseff of the ruling Workers' Party appeared shell-shocked by the result, a newly confident Ms Serra gave what sounded like a victory speech, and a beaming Ms Silva seemed to enjoy her new role as potential kingmaker.
"I want to congratulate Marina Silva. She has contributed to the democratic game in Brazil," Mr Serra told cheering supporters.
It was clear that Mr Serra, a former Sao Paulo state governor, would avidly court the Green Party over the next month to boost his chances in the run-off.
"My heart is totally environmentalist and Serra's is too," Mr Serra's vice-presidential running mate, Indio da Costa, said in an explicit overture to the Green Party.