Seoul, April 8 : South Korea's ruling Democratic Party suffered a crushing defeat in the by-elections for new Mayors of the country's two biggest cities, the National Election Commission said on Thursday. Oh Se-hoon of the main conservative opposition People Power Party won a landslide victory over Park Young-sun of the Democratic Party 57.50 per cent to 39.18 per cent in the mayoral by-election in Seoul, reports Xinhua news agency. In the mayoral by-election of the country's southeastern port city of Busan, Park Heong-joon of the People Power Party defeated Kim Young-choon of the Democratic Party by a wider margin 62.67 per cent to 34.42 per cent. The voter turnouts for Seoul and Busan reached 58.2 per cent and 52.7 per cent, respectively, topping 50 per cent for the first time in by-elections. It marked the first victory of the conservative bloc in about five years since the Democratic Party had won nationwide elections, including general elections in 2016 and 2020, local polls in 2018 and the presidential election in 2017. /IANS