Former Seoul Mayor Oh Se-hoon on Thursday won the main opposition party's ticket to run in the upcoming Seoul mayoral election seen as a barometer of public opinion ahead of the 2022 presidential election. 

Oh, who served as Seoul mayor from 2006-2011, won the People Power Party's primary for the April 7 Seoul mayoral by-election, solely based on a two-day public opinion poll, according to the polling results.

He beat former four-term lawmaker Na Kyung-won, former two-term lawmaker Oh Shin-hwan and chief of Seoul's Seocho Ward Cho Eun-hee. The former mayor won 41.64 percent of the support to pull off his surprise primary victory over Na, who had been leading all opinion polls. Na garnered 36.31 percent.

The party also picked Park Hyung-jun, a former chief presidential secretary for political affairs under former President Lee Myung-bak, as its candidate for the Busan mayoral by-election, also set for April 7.

Park won a landslide 53.4 percent of the support in the party's poll for the primary.

In a following acceptance speech at the party's headquarters in western Seoul, Oh said the election should serve as a "reckoning" for the incumbent liberal Moon Jae-in administration.

"This election needs to be one that makes a stern judgment against the reckless Moon government so that a message of warning from the depth of people's hearts will be nailed to the president's chest," Oh said in his acceptance speech.

He also pledged to achieve the unification of candidacies across the broader opposition bloc to boost chances of winning the election.

Oh, however, faces another uphill battle to compete with Ahn Cheol-soo, leader of the minor opposition People's Party, to unify their candidacies for the mayoral election.

Earlier this week, Ahn won a primary with independent candidate Keum Tae-sup, clearing the first hurdle in his bid to become a single candidate for the opposition bloc.

Both Ahn and the PPP agree on the need to field a single candidate representing the broader opposition bloc to raise the chances of winning the mayoralty.

Nonetheless, a thorny road lies ahead over how to choose a single candidate, with the PPP appearing to be wary about the possibility of losing to Ahn and becoming unable to field its own mayoral candidate as the biggest opposition party.

Currently, Ahn and Park Young-sun, the Seoul mayoral candidate from the ruling Democratic Party, are leading the opinion polls for the Seoul election. The latest polls conducted in February showed Ahn and Park are neck-and-neck in a hypothetical two-way competition for the Seoul mayoralty.

The upcoming mayoral by-election for Seoul, home to nearly 10 million of the country's total 52 million population, is deemed a critical barometer of public opinion ahead of the 2022 presidential election. 

The winner of the upcoming Seoul mayor election will serve out the remaining 14 months of the predecessor, late former Mayor Park Won-soon's four-year term. (Yonhap)