Topping Sunday’s tally was Mr. Duque, an American-educated protégé of the conservative Mr. Uribe. The former leader remains one of the country’s most popular politicians and a staunch ally of the American war on drug traffickers. Mr. Duque has echoed his mentor’s platforms.
He has also called Mr. Uribe Colombia’s “eternal president,” raising concerns among critics that if Mr. Duque were elected, Mr. Uribe would have outsize power or even seek to change the Constitution to return to the presidency.
María Isabel Vivero, a 42-year-old consultant who voted for Mr. Duque, said she felt he would stake out his own path. “Uribe will consult, but he won’t govern,” said Ms. Vivero, who vented frustration with Mr. Santos and said she had voted against the peace deal.
The second-place candidate, Mr. Petro, represents a starkly different option. The son of a rural schoolteacher, Mr. Petro joined a guerrilla group at a young age, later putting down his arms after a deal with the government in the 1990s and entering left-wing politics.
He is best known as the mayor of Bogotá, where he governed until 2015. He passed gun restrictions that reduced crime, lowered the price of public transportation and offered free water to the poor.
He was also polarizing: An effort to take control of the country’s waste management left the capital buried in trash and ended in his being removed from office for a period. On the campaign trail he has been reluctant to criticize Venezuela’s left-wing leaders for growing authoritarianism and food shortages, which have sent at least large numbers of refugees into Colombia.