Moon Jae-in, a lawyer-turned liberal politician, won the first regional primary of the Democratic United Party (DUP) Saturday, confirming his front-runner status as the main opposition party's presidential candidate in December's election.

   Moon, a former presidential chief of staff, won a total of 12,023 votes or 59.8 percent of the 20,102 valid votes cast during the DUP's primary in the southern island of Jeju, party officials said. Sohn Hak-kyu, a former DUP chief, was second with 4,170 votes or 20.7 percent.

   Some 36,000 party and citizen delegates registered to vote either through mobile phones or directly in polling stations during the Jeju primary that started at 5 p.m.

   "The results are much better than I expected," Moon said after the victory. "I think that this is thanks to voluntary participation of many civilians."

   Two other candidates -- former Trade Minister Chung Sye-kyun and former Gyeongnam Province Gov. Kim Doo-kwan -- are vying for the DUP ticket to stand against Rep. Park Geun-hye who was chosen earlier this week as the ruling Saenuri Party's candidate in the Dec. 19 election.

   South Jeolla Province Governor Park Jun-young has resigned, reducing the opposition party's candidate count to four.

   Moon is widely seen as a serious opposition contender to Park, a front-runner in opinion polls for the December 19 election.

   Recent polls, however, showed that Moon was behind Park and Ahn Cheol-soo, a popular software entrepreneur-turned-professor who has not yet announced his presidential bid.

   After Jeju, the DUP will also hold primaries in major cities and provinces, including Ulsan and Gangwon Province.

   The party is to designate its presidential nominee on Sept. 16, but a runoff will be held on Sept. 23 if none of the five contenders win a majority of the primary votes.

   The DUP lost the presidential election in 2007 after a decade of liberal rule in South Korea.

   South Korean President Lee Myung-bak's single five-year term ends in February and by law, he cannot seek re-election. (Yonhap News)