The former Army captain, dubbed "Tropical Trump" because of his nationalist agenda and anti-establishment tirades, won almost half the votes thanks to a surge in support sparked by growing anger at corruption and antipathy towards scandal-plagued traditional parties in Latin America's largest nation. They sent precisely the two candidates who most polarize the population to a runoff election, thus aggravating the country's problems still further.
With just three weeks until the runoff, Bolsonaro holds a commanding lead.
Bolsonaro fell short of the threshold required - 50 percent plus one vote - to avoid an October 28 run-off against his nearest rival, leftwing candidate Fernando Haddad.
By highlighting his ties to Lula, Haddad also played into the hands of Bolsonaro, who is riding a wave of anger at the Workers Party, which his supporters blame for widespread corruption, rising crime and recession.
In one of his last appeals to voters before Sunday's voting, Mr Bolsonaro tweeted that he would "defend the family and the innocence of children, treat criminals as such and not get involved in corruption schemes". Bolsonaro was shockingly stabbed at a rally in September and has been campaigning from the hospital on social media while recovering.
"He needs to say, 'Yes, we were culprits in this massive corruption scandal; we deeply, deeply regret what happened to Brazil, but we need to move on, ' " she said. "We have to remain mobilized".
Despite several controversial remarks on social issues, Bolsonaro is extremely popular in Brazil in large part for his strong opposition to socialism and promise to curb crime in a country that suffered 63,880 murders in 2017.
However, the PSL dominated Brazil's two biggest states, São Paulo and Rio de Janeiro, in the populous southeast.
"Bolsonaro is an example of honesty".
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Mr Bolsonaro is projected to take 45% of the vote and Mr Haddad 28%.
Nearly two-thirds of the electorate are concentrated in the more populous south and southeast of Brazil where its biggest cities, Sao Paulo and Rio Janeiro, are located - and where Bolsonaro holds a commanding lead.
Bolsonaro was expected to come out in front on Sunday, but he far outperformed predictions, blazing past competitors with more financing, the institutional backing of traditional parties and much more free air time on television. Recent polls suggest that 80 percent of Mr. Gomes' voters would drift to the Workers' Party candidate in the second round.
"A lot of young people are voting for him". He said he had already spoken to three other candidates to join forces against the right-winger. "We are on an upward trajectory and are confident that the Brazilian people want to distance themselves from socialism".
His words were a thinly veiled swipe at former President Luiz Inacio Lula da Silva, who dropped his fiery leftist rhetoric to win the presidency in 2002, dubbing himself the "Peace and Love" candidate.
Haddad can only win in the second round if he converts sceptics, galvanises Sunday's vanquished centrist candidates and their supporters and goes after his opponent on policy issues such as crime and security which, until now, he has appeared unwilling to grapple with, analysts said.
Bolsonaro won in four of the five regions of Brazil, only losing to Haddad in the northeast, a PT stronghold.
In Rio de Janeiro, Clara Gentil turned out to vote in Copacabana, wearing a T-shirt emblazoned with the message "Not him".