The front-runners in the Republic of Korea's election to replace outgoing President Moon Jae-in were neck and neck in the opinion polls as a total of four candidates were registered on Sunday, with the official campaign period set to kick off on Tuesday.

With polling day on March 9, the latest Realmeter poll published on Sunday indicated that Yoon Sukyeol from the opposition People Power Party held a narrow lead over the ruling Democratic Party's Lee Jae-myung, while other polls showed results swinging between the two.

According to the survey, Yoon garnered 41.6 percent of support to Lee's 39.1 percent.

The two other candidates: the People Party's Ahn Cheol-soo, a former medical doctor and entrepreneur who finished third behind Moon in the 2017 election; and Sim Sang-jung, a labor activist from the liberal Justice Party, who is also the sole female candidate, have single-digit ratings in the polls.

"From media coverage and public opinion polls it is very likely that either Yoon or Lee will become the next president of ROK, but it is unclear who will win the race," said Yu Qiang, a professor at the University of International Relations in Beijing, adding that whoever wins will not only matter to the country, but also will shape the future of Seoul's relations with Pyongyang, Beijing, Washington and Tokyo.

During their second TV debate held on Friday, Yoon and Lee spent most of the time engaging in verbal attacks over corruption allegations instead of serious discussions of policy issues.

Yoon accused Lee of involvement in corruption in land development projects and Seongnam FC soccer club based in Seongnam, Gyeonggi Province, where Lee used to serve as mayor. Lee fought back by mentioning Yoon's wife Kim Keon-hee, raising questions about her alleged involvement in a stock manipulation case related to Deutsch Motors, a BMW car dealer.

As a result, the chair of the debate had to step in at one moment to force them back to the topic of youth policy.

After the debate, an editorial in the Korea Herald commented that, whichever of the top two candidates is elected, people in the ROK "would be forced to live with a new leader facing a slew of corruption allegations and family-related scandals in the next five years".

Wang Chong, a distinguished professor at Zhejiang International Studies University and a senior researcher at the Charhar Institute, a foreign relations think tank, said Lee and Yoon proposed contrasting approaches on many issues.

According to Wang, the two have different perceptions of whether to prioritize Seoul's security ties with the United States or its economic ties with China.

"Of course they both support a strong US-ROK alliance, but they differ in terms of degree," Wang said, adding that Yoon is a pro-US politician who had proposed additional deployments as part of the US Terminal High Altitude Area Defense anti-ballistic missile defense system.

"Lee on the other hand, wants to maintain an equidistant policy between the United States and China, knowing that a worsening Beijing-Seoul relationship will only deepen domestic chasms like income inequality and youth unemployment," Wang added.

Yu said that although the two candidates both support dialogue and economic cooperation with the Democratic People's Republic of Korea, they differ on how they would approach the issue.

"Yoon wants to establish a trilateral diplomatic office between ROK, DPRK and the US and said he is open to signing a peace treaty and granting economic assistance if the DPRK denuclearizes first. Lee, as Moon's successor, would like to continue supporting diffuse reciprocity－engaging with the DPRK, even in the absence of a change in its behavior," Yu said.

According to Yu, Lee sees Seoul's role as a mediator between the US and the DPRK.

As for Tokyo's role, Park Jung-jin, a professor of international relations at Tsuda University in Tokyo, told local media that "Whether Lee or Yoon wins the race, it will be an opportunity for Seoul and Tokyo to reset ties."

Park said that Yoon, who is known for his pro-US policy, would approach the Japanese government "more proactively than Lee".

"But I find it hard to be optimistic about the outlook for bilateral relations, at least in the near term, given that the comfort women and wartime labor issues have become so politicized in the two countries," Park said.