Jair Bolsonaro, a presidential candidate in Brazil often compared to U.S. President Donald Trump, won the first round with 46 percent of the vote, just short of the 50 percent required to prevent a run-off.
Haddad, a former education minister and one-term mayor of Sao Paulo, had portrayed a vote for him as a show of support for Workers Party founder and former President Luiz Inacio Lula da Silva, whom many voters associate with good economic times and falling inequality.
Supporters of presidential front-runner Jair Bolsonaro celebrate Sunday's election numbers.
"We are seeing a conservative or centre-right tsunami that has produced the biggest change in Brazil's political landscape for the past few decades", Stuenkel said.
"But attacks on Bolsonaro have tended to strengthen him", she added. In 2014, the majority of Brazil's north-east voted for Worker's Party candidate Rousseff in the presidential election (which she went on to win), with some states in the region giving her almost 80% of the vote. The vote will be held on October 28. That clears out powerbrokers who could have extracted costly concessions to pass Bolsonaro's agenda. Since the vote, posts have circulated on Facebook lauding the north-east for potentially saving the nation and encouraging people to report abusive posts about the region's inhabitants.
Experts predict political pyrotechnics between now and then as the two men lock horns on their dramatically different visions for Brazil.
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Flake and Collins voted in favour of Kavanaugh's confirmation, while Murkowski opposed it but asked to be recorded as "present". The fourth clerk, Sara Nommensen, is a former student of Kavanaugh's from Harvard Law School who previously worked at the U.S.
Many analysts thought Mr Bolsonaro would win the first round of voting but face a runoff between the two top vote-getters which he would he lose. Bolsonaro has already stated that he will accept no other result than his election while Vladimir Safatle, a renowned professor from the University of São Paulo, has warned that "there is a military coup in process in Brazil now".
His promises to give police freer rein, his criticism of the social movements and reforms that have attempted to make Brazil more inclusive and equal, and his frequent praise for Brazil's 1964-1985 military dictatorship have raised concerns that a Bolsonaro government will erode democratic values and rule with an authoritarian hand.
Haddad has also spent much time arguing that da Silva, his mentor, was unfairly jailed - a strategy aimed at attracting voters who still feel strong affection for da Silva, known in Brazil simply as Lula.
"This is a victory for honest people who want the best for Brazil", said Bianca Santos, a 40-year-old psychologist who gathered outside a hotel where Bolsonaro was watching the returns. Bolsonaro has been endorsed by the fifth-place finisher, potentially handing him nearly half the votes he needs for a win.
But Haddad is facing a tough challenge, not least because he is running as a stand-in Lula.
Bolsonaro has promised to reverse a crime wave that brought a record 63,880 deaths in 2017, the most of any country in the world, by rolling back gun controls and making it easier for police to kill.