BOGOTA (Reuters) - Right-winger Ivan Duque, who wants to overhaul a peace deal with Marxist rebels, won Colombia’s first-round presidential election on Sunday, setting up a runoff next month with leftist Gustavo Petro, who has pledged to confront privileged elites.

The first election since the peace accord was signed with the Revolutionary Armed Forces of Colombia (FARC) in 2016 now heads for a June 17 runoff to select the successor to President Juan Manuel Santos, who won the Nobel Peace Prize for ending the five-decade-old conflict.

Duque, 41, has pledged to toughen the terms of the peace deal and ensure former rebels pay for their war crimes, while Petro has provoked alarm among investors with pledges to overhaul Colombia’s orthodox economic policy and redistribute wealth from the rich to the poor.

With almost all polling stations having reported results, Duque led with 39.1 percent of the vote, as expected, while Petro was a distant second with 25.1 percent.

It was the first time in Colombia’s modern history that a leftist candidate has reached the second round of a presidential poll.

Center-left mathematician Sergio Fajardo came a close third, with 23.8 percent, but he declined to endorse either candidate for the second round, saying his voters would make up their own minds.

Campaigning in the traditionally conservative South American nation has been marked by acrimonious accusations that Duque and Petro - from opposite ends of the political spectrum - risked dragging the country back to the battlefield or collapse the economy with socialist policies.

But with Fajardo and the other losing candidates committed to the peace process, Duque may need to soften his stance against the FARC to attract wavering voters, while emphasizing the dangers he says Petro poses for the economy.

Petro, 58, in turn, may seek to allay concerns that his economic policies would lead to a crisis of the kind unfolding across the border in socialist-run Venezuela.

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“I’m worried ... Populism is strengthening,” said Nicolas Goyeneche, a 28-year-old student, wearing a Duque hat at the candidate’s celebration party in the capital Bogota. “But in the second round, we’ll beat populism.”

Business-friendly Duque was handpicked by hardline former President Alvaro Uribe, who is seen as the power behind his campaign. As well as impose tougher punishments on former FARC fighters, Duque has promised to cut corporate taxes and support oil and mining projects.

“We don’t want to shatter the agreement, we want to make it clear that a Colombia of peace is a Colombia where peace meets justice,” he said as supporters waved balloons and chanted his name.

“Those most responsible must truly make amends to Colombia ... because if we don’t have that, peace will never be lasting.”

Under the terms of the 2016 peace deal, thousands of rebels demobilized and the group became a political party. But the accord angered many who believe FARC commanders should be in prison and not in Congress.

Some areas abandoned by the FARC have suffered an increase in fighting between criminal gangs and a remaining guerrilla group, the National Liberation Army (ELN), over valuable illegal mining and drug trafficking territories.

Colombia’s production of coca, the raw material for cocaine, has risen sharply, stirring concern in Washington.

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SPECTER OF VENEZUELA

“Mathematically there’s a fact - the advantage Duque had over us has diminished,” said Petro, surrounded by his family as supporters cheered. “Have certainty that we’re going to win, that Colombia’s history can be changed.”

Petro, a combative populist who was once a member of the now defunct M19 rebel group, supports the peace deal. But some of his economic policies spook investors and have prompted rivals to compare him to former Venezuelan President Hugo Chavez.

A flood of hundreds of thousands of Venezuelans streaming across the border to flee shortages of food and rising crime has alarmed many Colombians and prompted Santos’ outgoing government to appeal for international aid.

Petro has promised to take power away from political and social elites who he says have stymied progress, as well as carry out a complete economic overhaul.

At his election night party in the capital, communist party militants waved red flags above the crowd.

“When we talk about defeating poverty, we’re not talking about impoverishing the rich, but about enriching the poor,” Petro said.

In a country where oil and coal are the top export earners, Petro’s pledges to end extractive industries and shift the focus of state-run oil company Ecopetrol to renewable energy have dismayed business leaders.

Petro voters are excited by the possibility the right-wing status quo could be overhauled and a leftist president installed for the first time in Colombia’s history.

Polls suggest the end of the FARC conflict has shifted voters’ priorities to inequality and corruption from security issues - opening the door to the left for the first time.

“I’m very happy,” said Diego Rodriquez, a 38-year-old sociologist. Not only for the passage of Petro to the second round, but because the center-left represented by Petro and Fajardo has more votes than the candidate of the right.”

Graphic tmsnrt.rs/2rAQ4l1 on Latin American elections