The May 9 election has shaped up to be a duel between the longtime rivals, with Ahn posing a growing challenge to Moon since early this month.

Hong Joon-pyo of the conservative Liberty Korea Party stood in third place with 7 percent, trailed by Sim Sang-jeung of the minor progressive Justice Party and Yoo Seong-min of the splinter conservative Bareun Party at 3 percent each.

"Unlike other candidates, Ahn Cheol-soo's approval rating far exceeds the approval rating of his party," the pollster said. "In other words, at this point, Ahn has a considerable following outside the support base of the People's Party, which means there is a greater level of uncertainty or vulnerability compared with other candidates."

Support for Ahn's party stood at 24 percent, compared to 41 percent for the Democratic Party.

By region, Moon beat the former software mogul in the liberal stronghold of Gwangju and the surrounding Jeolla provinces, as well as in the southeastern region covering Busan, Ulsan and South Gyeongsang Province. Ahn, meanwhile, posted nearly double Moon's approval rating in the conservative stronghold of Daegu and nearby North Gyeongsang Province.

The two were neck and neck in Seoul, the adjacent area of Incheon and Gyeonggi Province, and the central swing region of Daejeon, Sejong and Chungcheong.

Moon led Ahn among voters aged 19-49, but trailed his rival among those aged 50 or above.

Conservatives backed Ahn over Moon by 48 percent to 17 percent, liberals supported Moon over Ahn by 66 percent to 23 percent, and moderates were equally divided at 40 percent each.

Voters said Moon appears to be the most capable of all candidates to handle inter-Korean relations, national emergencies and social and welfare issues. Ahn topped the list for change and reform.

The survey was conducted on 1,010 adults nationwide and had a margin of error of 3.1 percentage points at the 95 percent confidence level. (Yonhap)