Despite being the anti-corruption champion, Hernandez is accused of improperly awarding contracts while he was the mayor of Bucaramanga, from which his son benefited financially.
Since winning in the first round on May 29, Petro has been trying to get the votes of the undecided by appealing to women and the younger population.
Hernandez, who has drawn comparisons with former US President Donald Trump, has been securing votes where he has built his prominence: TikTok and YouTube. He has repeatedly refused to attend debates despite the insistence of his contender.
Although Petro obtained 40% of the votes against 28% for Hernandez in the first electoral round, Hernandez intends to capture a majority of votes from the candidates who lagged behind in May.