The far-right frontrunner to become Brazil’s next president has insisted he will not moderate his combative rhetoric or become a “peace and love” candidate as he continues his push to become leader of Latin America’s largest democracy.

Jair Bolsonaro, a pro-dictatorship former army captain, secured nearly 50m votes in the first round of the presidential election on Sunday – about 46% of the total and just short of the outright majority needed to claim victory. The 63-year-old populist will now face off against the runner-up, the Workers’ party candidate, Fernando Haddad, in a second-round runoff on 28 October.

Experts predict political pyrotechnics between now and then as the two men lock horns on their dramatically different visions for Brazil. In a 20-minute interview with the Brazilian radio station Jovem Pan on Monday, his first since the previous day’s triumph, Bolsonaro said he hoped to return to active campaigning soon, after his recent near-fatal stabbing, and would continue to insist on being tough on crime and tough on the left.

“Our discourse will basically stay the same – one of union. We need to unify Brazil, to pacify it,” he said. “We have flirted too much with the left over the past 20 years. It’s time to move to the centre-right.”

Asked whether he would continue his “conservative preaching” or lean towards the centre ground to attract new voters, Bolsonaro said: “I can’t just suddenly become ‘Little Peace and Love Jair’ … I’ve got to carry on being the same person.

“Of course, we sometimes use synonyms,” he said of his reputation for making incendiary and offensive comments about Brazil’s black and gay communities and women. “I used to use swear-words now and again. I don’t any more.”

Glauco Peres, a political scientist at the University of São Paulo, predicted that in the absence of concrete policy proposals, fear would remain Bolsonaro’s main weapon as the second round approached.

“I think Bolsonaro will carry on doing what he’s doing. I don’t think he has to change much,” Peres said. “He’ll keep hammering away at this idea of fear … that the PT [Partido dos Trabalhadoresor Workers’ party] represents a step backwards into corruption scandals and having criminals in government.”

The far-right candidate did precisely that on Monday, as Haddad travelled to southern Brazil to meet with his political patron, the jailed former president LuizInácio Lula da Silva, to discuss his second-round strategy. “It’s up to you,” Bolsonaro tweeted to his 1.6m followers. “You can be governed by somebody who is clean, or by the stooge of someone who is in prison for corruption!”

Experts and supporters say one of Haddad’s most urgent tasks, if he is to roll back what one newspaper called Bolsonaro’s “conservative tsunami”, is to build an anti-Bolsonaro alliance stretching across the political spectrum.

“In order to achieve the miracle of turning this around, Haddad’s mission is now to form a democratic front,” Ricardo Kotscho, a veteran journalist with ties to Lula and the PT, wrote in an essay pondering how Brazil might be saved from the “tragedy” of “Bolsonarismo”. “If everyone comes together, it will be possible to reverse Sunday’s reactionary wave,” and prevent Brazil returning to “the uniformed darkness of the past”.

To do that, Kotscho said Haddad needed to have “the grandeur to seek the support of all those who didn’t leap into the Messianic captain’s boat … in order to expand his electorate and isolate the far right.”

On Sunday night, Haddad signalled immediately that he would look to build such a bloc. “We want to bring together Brazil’s democrats,” he told supporters in a speech that concluded with the rally crying: “Long live Brazil! Long live democracy!”

But securing that support may not be straightforward – or even effective.

“I just don’t think it will work,” said Brian Winter, editor-in-chief of Americas Quarterly. “If a huge group of well-known politicians lines up behind Haddad, all Bolsonaro has to do is point at them and say: ‘See! The corrupt establishment is with him’ – and it’s over.”

“People [have] decided to deposit their hope in Bolsonaro. They see in him the promise of an end to the chaos of the last four years. And in that mindset, Bolsonaro becomes the future and Haddad is the past.”

Monica de Bolle, the director of Latin American studies at Johns Hopkins University, said she expected Bolsonaro to come under heavy fire from Haddad and other defeated presidential candidates over the coming weeks, above all for his disdain for democracy.

“But attacks on Bolsonaro have tended to strengthen him,” she added. “So I’m not quite sure how that works.”