Brazil's far-right president Jair Bolsonaro has come in second behind his left-wing rival denying him an outright victory in the country's election.
The shock result went against polls which suggested Luiz Inacio Lula da Silva would secure a majority in the first round of the contest.
However, Bolsonaro won 43.2 per cent of the ballot, compared with Lula's 48.4 per cent share, meaning another vote will take place on October 30.
The race proved tighter than most surveys suggested, revitalising Bolsonaro's campaign after he insisted that polls could not be trusted.
If he pulls off a comeback, it would break with a wave of victories for left-wing candidates across the region in recent years, including Mexico, Colombia, Argentina and Chile.
Adding to tensions in Brazil, Bolsonaro has made baseless attacks on the integrity of Brazil's electronic voting system and suggested he may not concede if he loses.
On Sunday night, he sounded confident victory was within reach and avoided criticism of the voting system.
"I plan to make the right political alliances to win this election," he told journalists, pointing to significant advances his party made in Congress in the general election.
Bolsonaro's right-wing allies won 19 of the 27 seats up from grabs in the Senate, and initial returns suggested a strong showing for his base in the lower house.
The support for Bolsonaro and his allies, which added to pressure on Lula to tack to the centre, led bankers and analysts to expect a boost for Brazilian financial markets on Monday after Sunday's surprising result.
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Lula put an optimistic spin on the result, saying he was looking forward to another month on the campaign trail and the chance to debate Bolsonaro head-to-head.
Inside his campaign, however, there was clear frustration that he had fallen short of the narrow majority forecast in some polls, along with weak results in state races outside of his party's traditional north-eastern stronghold.
A campaign source said: "There was a clear movement of votes in the southeast, beyond what the surveys and even the campaign managed to detect."
Support for distant third and fourth place finishers also fell short of recent surveys, suggesting some of their backers may have shifted to Bolsonaro when it came time to vote.
Centrist Senator Simone Tebet, who got four per cent of votes, and centre-left former lawmaker Ciro Gomes, who got three per cent, both said on Sunday night they would announce decisions about endorsements in the coming days.
With the momentum in Bolsonaro's favour, Lula may need all the help he can get.
