(Bloomberg) -- Colombia’s presidential election this month is no longer a two-horse race after support surged for the third-placed candidate, a poll found.  

Rodolfo Hernandez, 77, a former construction magnate and mayor of the provincial city of Bucaramanga, saw his support more than double to 19.1% ahead of the May 29 first round, according to a poll by Centro Nacional de Consultoria, or CNC, published by Semana magazine Thursday. 

A CNC poll published last month showed Hernandez with just 9.6% backing. 

Leftist Senator Gustavo Petro, 62, remained the frontrunner, with 35.8% support. Federico Gutierrez, 47, a conservative former mayor of Medellin, was in second place with 20.8%. 

All other major polls published recently had indicated a probable second round between Petro and Gutierrez. 

Hernandez is campaigning on a pledge to crack down on corruption, and has rejected alliances with Colombia’s main political parties. 

In the likely event of a runoff vote on June 19, Hernandez and Petro would be tied with 40.5%, the poll found. In a second round against Gutierrez, Petro would win by nine percentage points, according to the survey. 

Poll of 4,412 people conducted May 13-19 has a margin of error 1.5 percentage points.

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