Moon Jae-in, the former leader of the Democratic Party of Korea, got a ratings boost following the second televised debate held among the five main presidential hopefuls earlier this week.
The latest polls show he's widened his lead over his opponent Ahn Cheol-soo, the co-founder of the minor opposition People's Party, who saw his ratings fall after the debate.
A poll by Gallup Korea released Friday shows Moon with 41-percent support to Ahn's 30-percent.
That's a gap of 11-percentage-points, up from a 3-percentage-point gap in the same poll last week.
Another poll by Research and Research shows Moon with more than 30-percent to Ahn's 20 -- a near 10-point gap.
In that poll, Hong Joon-pyo of the conservative Liberty Korea Party also got a post-debate bump, bringing him up into the double digits.
Since the debate, there's been a noticeable shift among voters in the traditionally conservative stronghold of Korea's southeastern region of Daegu and Gyeongsangbuk-do Province, with the ratings for Hong inching up, as those of Ahn plunged.
The drop in support for Ahn is attributed to an increase in negative campaigning at the start of the official campaign period.
Ahn and his wife have been accused of pressuring his National Assembly aides for personal favors, later prompting the couple to offer an apology.
Ahn is also struggling against allegations of tax evasion and embezzlement of funds from his computer software company Ahnlab.
Ahn has denied the charge and the company has defended him, saying it will pursue legal action against those spreading what it calls false rumors.
Kim Ji-yeon, Arirang News.