Conservative political newcomer Ivan Duque has been elected president of Colombia.
With nearly all votes counted. Mr Duque has 54% with his rival Gustavo Petro on 41.8%.
The result raises questions about the future of a historic but controversial peace deal with Farc rebels.
Mr Duque, who is supported by former President Alvaro Uribe, has said he will overhaul the 2016 agreement which gave the rebels places in Congress.
The orthodox economist also says he will revisit crimes allegedly committed by the rebels during the brutal five-decade conflict with the government.
Mr Duque is viewed as the business-friendly choice because he wants to cut taxes and boost investment, raising money by shrinking the state.
Fear of the left won out
Katy Watson, BBC Latin America correspondent, Bogotá
In conservative Colombia, it’s another win for the right. Rival Gustavo Petro put up a good fight and the fact that a left-wing candidate got to the second round was something Colombia hadn’t seen before.
The peace deal meant that left-wing politics became more acceptable and not associated with violence like in the past.
But in the end, the continued fear of the left in this country won out. Mr Duque was seen as the safer pair of hands to lead after more than 50 years of conflict.
With his campaign promise of changing the agreement struck with the FARC rebels, there’s a lot of uncertainty about what that will mean for the country’s prospects of long-term peace.
Voters in the country were presented with a stark choice between Ivan Duque and the leftist ex-guerrilla Gustavo Petro.
Mr Petro’s campaign featured promises about creating a more equal society and ensuring people have access to health and education.
He also pledged to take on political elites and redistribute land to the poor.
But the former Bogota mayor, who supports the peace deal, accepted defeat on Sunday evening.
“Eight million free Colombians taking a stand. There is no defeat here. For now we won’t be the government,” he said on Twitter.