Brazilian President Luiz Inácio Lula da Silva and Senator Flávio Bolsonaro began seeking new allies this week for the high-stakes October 25 presidential runoff, with a government proposal to shorten the working week quickly emerging as the first battleground of the second-round campaign.

Bolsonaro, the eldest son of convicted former president Jair Bolsonaro, took 47.03% of valid votes in October 4’s first round against 45.16% for the leftist incumbent, a lead of about 2.2mn votes. The right-wing Liberal Party (PL) also performed strongly in Congress and in state governments.

Soon after the vote, Bolsonaro won the endorsements of two right-wing rivals eliminated in the first round, former Goiás governor Ronaldo Caiado, who won 2.18% of the vote, and former Minas Gerais governor Romeu Zema, who received 0.27%.

Caiado, of the PSD party, was due to meet Bolsonaro to formalise his support. "I vote against the Workers' Party (PT) and for Flávio Bolsonaro," Zema said in a social media post.

Former President Michel Temer also backed Bolsonaro, saying Brazil "wants a different path" from the one offered by Lula. Lula has repeatedly called Temer a "coup leader" for taking office after Dilma Rousseff's impeachment in 2016.

PL president Valdemar Costa Neto said the party would seek the support of the centre-right União Brasil, Republicanos and Progressistas (PP) parties, which hold 128 seats in the lower house and did not back any candidate in the first round.

Author and psychiatrist Augusto Cury, who won 2.89%, and Renan Santos, who took 2.24%, said they would not endorse either candidate for now.

Lula, who admitted surprise at the first-round result, met campaign officials, ministers and allies on October 5 to plan his runoff strategy. He said he would focus on persuading the more than 30mn Brazilians who did not vote and would take part in televised debates, which he had avoided before the first round.

"It is our responsibility to revive their interest in participating in the elections," Lula said.

The president also sought to take on two issues central to his rival's campaign. On security, he acknowledged that criminal factions had "won the day" so far and vowed to step up the fight against organised crime.

"Criminals must go to prison," Lula said, urging the Senate to approve his government's constitutional reform on public security.

He also hardened his criticism of the Supreme Court, saying the "promiscuity" of several justices with jailed banker Daniel Vorcaro, at the centre of the Banco Master fraud scandal, had to stop.

The campaign's first major clash came over a proposed constitutional amendment to end Brazil's six-day working week, known as the 6x1 schedule, which the seasoned leftist leader is championing as a key re-election pledge.

Bolsonaro called the timing of the Senate vote "opportunistic" and said he had a better plan to let workers choose their own working hours.

"I have a proposal that is infinitely better than the one currently on the table, which is to give workers the freedom to choose their own working hours," Bolsonaro told reporters in Brasília, according to Estadão.

"The Lula government, in four years in office, didn't do anything. Now, in the middle of the second round, he's opportunistically trying to make a move, thinking that this will win him votes," he said.

Lula responded by calling the vote a test for Bolsonaro's party. "When the Senate starts voting, the mask will fall. We'll see who truly wants the people to have a more dignified life, rest more, and take better care of their families," Lula said, according to Valor.

Institutional Relations Minister José Guimarães said Senate President Davi Alcolumbre was "determined" to put the amendment to a vote before the runoff. "I want to see Flávio Bolsonaro's group vote against it," he said.

Lula's pledge to join debates marks a shift after both frontrunners skipped every televised debate before the first round. In an editorial on the eve of the vote, newspaper Folha de S.Paulo said both candidates had "disrespected the electorate" by refusing to debate and argued the election would benefit from a second round.

Investors, meanwhile, cheered Bolsonaro's first-round lead. The Bovespa stock index jumped 7.7% to a record high on October 5, while the real strengthened 4.1% to BRL5.00 per dollar. Shares in state-owned oil company Petrobras (B3: PETR4; NYSE: PBR) rose 8.1% to an all-time high.

Despite not openly endorsing either candidate, US President Donald Trump also welcomed the result. "It's a big victory -- close, but very, very big victory. Amazing," Trump told reporters at the White House.