Three heavyweights within the minor opposition People's Party advanced to the final round of the presidential primary Friday ahead of the May presidential vote.

South Korea is set to hold an early presidential election on May 9 following the dismissal of President Park Geun-hye over a corruption scandal. Chances are high that voters will gravitate toward the liberal bloc, including the People's Party, to punish the conservatives for their failed administration.

Former party leader Rep. Ahn Cheol-soo, former main opposition leader Sohn Hak-kyu and Vice National Assembly Speaker Rep. Park Joo-sun won the most votes in a six-way race to pick the three finalists for the party nomination.

Ahn presented himself as the most powerful candidate among them to challenge frontrunner Moon Jae-in of the Democratic Party.

"The coming presidential election is a race between Ahn Cheol-soo and Moon Jae-in," Ahn said. "I will return (your support) with victory."

The former software mogul competed against Moon ahead of the 2012 presidential election before eventually dropping out to back his rival's bid. Moon currently garners over 30 percent approval ratings in presidential polls.

Sohn, a seasoned politician with a considerable following in both the left and right, pledged to push through reforms and forge national unity.

"Who will change our country? Who will beat Moon Jae-in? I, Sohn Hak-kyu, will," he said. "The People's Party must unite and grow. I, Sohn Hak-kyu will achieve a grand alliance of reform and a joint government of reform."

Park, meanwhile, boasted a firm political foundation in the southwestern Jeolla region, the liberal stronghold.

"As the only candidate hailing from Honam (Jeolla), Park Joo-sun, the legitimate son of Honam, must become the presidential nominee," he said. "If I become the nominee, I will work for national unity and an era of national reconciliation and pursue a grand alliance as a realistic strategy for the People's Party to take power."

The third-largest party in the unicameral parliament has come under pressure to form a coalition with the minor conservative Bareun Party to boost their chances of winning the election.

Friday's vote was held at the National Assembly among 505 party lawmakers and officials, regional chapter heads, and local government chiefs and council members belonging to the party.

The liberal party will nominate its standard-bearer on April 4. (Yonhap)