Bolsonaro, a former Army captain and veteran lawmaker, almost won the presidency outright on Sunday, taking 46 percent of votes against leftist Fernando Haddad's 29 percent, part of a swing to the right in Latin America's largest nation.
Bolsonaro of the Social Liberal Party narrowly missed out on the outright majority required for first round election success on Sunday, winning 46 percent of the vote.
Haddad, the candidate for the Workers' Party (PT), who was selected to replace Lula Da Silva on the ballots in September after a court barred the convicted former leader from running, received 29 percent of the vote.
He expressed confidence that Bolsonaro would easily win the presidency later this month, saying that many who voted for other candidates on Sunday want to block the PT, which held the presidency from 2003 to 2016, from returning to power.
If Bolsonaro wins a runoff election, they "wouldn't be surprised" if the index reached 105,000, with stocks of state-controlled companies, consumption and real estate among the largest winners.
Dubbed a "Tropical Trump" by some pundits because of his nationalist agenda and anti-establishment tirades, Bolsonaro was swept from the political margins this year by a wave of antipathy toward scandal-plagued traditional parties.
"Anyone who lives in Brazil knows that life got worse under the Workers' Party, especially for the middle class", she said. Bolsonaro has a history of making racist, misogynistic and homophobic comments.
Critically, he's upended the traditional political campaign approach, staying clear of public debate over big policy issues and instead mobilising social media to appeal directly to voters with plainly worded pledges.
Preliminary results showed unexpectedly big congressional wins by Bolsonaro proxies including former military police Major Olimpio Gomes, his campaign manager in Sao Paulo, who was elected to the Senate.
He promised to roll back the economic reforms that he says eroded workers' rights, increase investment in social programmes and bring back the boom years Brazil experienced under his mentor, Luiz Inacio Lula da Silva.
For voters, Bolsonaro and Haddad represent starkly different visions for the future. He has promised to fight long-standing inequalities, scrap a major labour reform passed past year and invest more in education.
With the field reduced to two candidates, some analysts see Haddad as the natural inheritor of numerous centrist votes that will be up for grabs, but the scale of Bolsonaro's first-round success means that Haddad will have little room for manoeuvre.
Bolsonaro has painted a nation in collapse, where drug traffickers and politicians steal with equal impunity, and moral rot has set in.
Many voters, already disillusioned with their democracy, said they felt trapped by the choice between the two front-runners, a sentiment likely to deepen in the weeks to come.
"I think Bolsonaro will carry on doing what he's doing. So I chose to vote for Bolsonaro, who is the only one who can block the return of the Workers' Party". "A miracle would be for Bolsonaro to see the light and govern the country for the people, for him to become less radical".