Less than a month before the April 7 by-election to choose Seoul’s next mayor, Oh Se-hoon, a former mayor and the sole candidate from the main opposition People Power Party, is ahead of both of the other major candidates -- People’s Party Chairman Ahn Cheol-soo and Park Young-sun, former minister of SMEs and startups and the sole candidate from the ruling Democratic Party of Korea -- a poll showed Tuesday.

According to a Realmeter survey of 1,030 Seoulites aged 18 or older on March 13 and 14, Oh gained 35.6 percent approval in the three-way race, coming out 2.3 percentage points ahead of Park (33.3 percent). Ahn received approval from 25.1 percent of respondents.

Oh received strong support from those aged 60 or older (45.2 percent), those in their 50s (42.8 percent), conservatives (55.1 percent) and supporters of the People Power Party (67.8 percent).

Park received overwhelming support from the Democratic Party’s supporters (83.9 percent). She also got significant support from those in their 30s (40.6 percent) and from self-described liberals (63.9 percent).

Ahn’s support was notable among people 18-29 years old (34.9 percent), middle-class people (31.4 percent) and People’s Party supporters (56.5 percent).

In the virtual bilateral race between the opposition and ruling parties, the opposition party’s single candidate took the lead by a large gap.

Oh enjoyed 54.5 percent support, putting him 17.1 percentage points ahead of Park. Ahn, at 55.3 percent, was 17.5 percentage points ahead of her.

As for who should run as the single opposition candidate, 39.3 percent of the respondents picked Oh while 32.8 percent picked Ahn.

The approval ratings for political parties in Seoul stood at 35.4 percent for the People Power Party, 31.2 percent for the Democratic Party and 9.5 percent for the People’s Party.

In another survey done Saturday by PNR Research on 803 men and women aged 18 or older living in Seoul, 46.2 percent of the respondents said they would vote for Oh in a bilateral race with Park.

Meanwhile, the two opposition candidates, Oh and Ahn, appear determined to join forces.

The two candidates held a presentation Monday detailing their policy goals for the Seoul government and agreed that for the opposition bloc to win, a three-way race was unfavorable. They vowed to unify their campaigns before March 19.

On Tuesday, Ahn said if he becomes mayor, he plans to pursue a merger with the People Power Party after getting agreement from party members.

By Shin Ji-hye (shinjh@heraldcorp.com)