Former Prosecutor General Yoon Seok-youl, Rep. Hong Joon-pyo, former opposition lawmaker Yoo Seong-min and former Jeju province Governor Won Hee-ryong were announced as the four remaining contenders in the PPP's presidential primary.
Friday's result was based on a survey that combined a national poll and a separate one on registered PPP members.
The standings of the remaining contenders were not disclosed.
Of the pool of eight contenders, Choe Jae-hyeong, former chief of the Board of Audit and Inspection, Representatibe Ha Tae-keung, former Incheon Mayor Ahn Sang-soo and former Prime Minister Hwang Kyo-ahn failed to make it to the top four.
Yoon and Hong, competing for the lead in the PPP primary, were expected to comfortably make it to the next round, while Yoo, who made headlines lately for his confrontations with the former top prosecutor in television debates, was also largely predicted to make the cut Friday.
The latest round was watched closely to see who would make it to the supposed fourth spot, for which Won and Choe have aggressively competed.
The ruling Democratic Party, meanwhile, is in the near final stretch of its presidential primary, in which Gyeonggi Province Governor Lee Jae-myung is the dominating lead.
The race is scheduled to wind up with a primary in Seoul on Sunday.
The presidential election is scheduled for March 9, 2022.