More than a day after Brazil's electoral chief declared Luíz Inácio Lula da Silva the winner of the presidential election, defeated incumbent Jair Bolsonaro has yet to concede.
The far-right president is said to have gone to sleep after he narrowly lost to his left-wing arch rival.
His silence is raising concern that he may not accept the result.
He has in the past cast unfounded doubts on the voting system.
Combative statements from Mr Bolsonaro in the past - such as that "only God" could remove him from office - mean there is a tense wait for him to appear in public.
Brazil's Superior Electoral Court announced that Lula had won the run-off of the presidential election just minutes before 20:00 local time (23:00 GMT) on Sunday.
With all the votes counted, Lula had 50.9% of the valid votes against Mr Bolsonaro's 49.1%.
In his victory speech, Lula touched on the political rift running through Brazil which further deepened during a bitterly fought and often acrimonious election campaign.
"This country needs peace and unity. This population doesn't want to fight anymore," he said, promising to govern for all Brazilians and not just for those who had voted for him.
Congratulations have poured in from across the world, including from the leaders of Britain, China, France, India and Russia. US President Biden said the win came "following free, fair and credible elections".
But even though it is traditional for the losing candidate to phone the winner, and to make a statement acknowledging their defeat, Mr Bolsonaro has so far remained silent.
People close to the president said that after the result he had "gone to sleep" at the presidential palace in the capital, Brasilia.
In the morning, a presidential adviser and Mr Bolsonaro's vice-presidential running mate were seen arriving at the palace, but it is not clear if he met them and what was said.
Later, Mr Bolsonaro was seen leaving the palace and travelling to the building where his official office is located.
Brazilian media are reporting that everything has been set up for a presidential news conference but that no one knows if one will be held in the next hours.
Meanwhile, close allies of Mr Bolsonaro have acknowledged Lula's election win, among them the powerful leader of the lower house of Congress, Arthur Lira, and Tarcísio de Freitas, who is the new governor of São Paulo state.
The strong backing Lula has received both at home and abroad so quickly after his win will make it more difficult for Mr Bolsonaro to contest the result, analysts say.
However, an uncooperative outgoing president could make the two-month transition period until Lula is due to be sworn in on 1 January 2023 a lot bumpier.
Some disruption has already been caused by lorry drivers loyal to Mr Bolsonaro, who have blocked roads in at least 13 states.
A number of the roadblocks have reportedly been cleared but the remaining ones are causing considerable disruption on major roads.
Lula has not talked about his defeated rival since his victory speech and has instead held a meeting with the Argentine president.
His party says he will speak to US President Biden on the phone later today.
BBC
Russia's unmanned Luna-25 spacecraft has crashed into the Moon after spinning out of control, officials say.
Donald Trump has confirmed that he will not take part in Republican presidential debates with his rivals in the race for the White House.