STORY: Colombia is heading to a presidential runoff after a tight first round on Sunday, with right-wing outsider Abelardo De La Espriella facing leftist senator Ivan Cepeda.

Early results show a narrow gap of almost two percentage points between them, with De La Espriella slightly ahead at over 43% of the votes.

Cepeda and his allies are holding off on reacting, citing concerns about the vote count. Here's what he told supporters:

"There is a discrepancy that we want to verify regarding the electoral roll, and that is not just any discrepancy. We are talking about 885,000 people, or ID numbers."

President Gustavo Petro, a Cepeda ally, also says he will wait for official review by judges.

As of 8:15 p.m. local time, roughly half the votes had been certified, according to official tallies.

The race has centered on security, the economy and populist policies for the country.

De La Espriella is a 47-year-old lawyer who has portrayed himself as an outsider free from political baggage.

Speaking from a boat, he struck a confident tone while thanking his supporters:

"In this second round, I will be at the forefront of this battle. I will stand as Colombia's finest warrior to defend our democracy until death."

The lawyer built his campaign on a tough stance against armed groups, the construction of 10 megaprisons, poverty reduction through better education, healthcare and housing for the nation's poorest.

Cepeda, meanwhile, has promised to pursue peace with illegal armed groups through negotiations.

Though that approach has brought little progress under Petro. 

He also plans to deepen reforms meant to reduce inequality and poverty, such as raising taxes on high-income earners.

Surveys suggested the lawmaker will face a much tougher challenge in the second round, once right-leaning voters no longer have multiple candidates to choose from.

However low turnout from Sunday's vote may give the candidates room to maneuver, if they can convince more supporters to vote in the runoff on June 21.