SEOUL, Feb. 2 (Xinhua) -- Moon Jae-in, former head of the biggest opposition Minjoo Party, kept his top post by a wide margin after former UN chief Ban Ki-moon dropped his bid for presidential race, local media reported on Thursday.

Ban, the career South Korean diplomat whose second, five-year tenure in the top UN post terminated at the end of last year, returned to his home country three weeks earlier.

He was welcomed in the conservative camp as the powerful presidential contender, but he abruptly pulled out of the presidential race on Wednesday as his support scores tumbled following the lunar New Year's holiday.

According to a survey of 1,000 voters conducted Wednesday to reflect Ban's withdrawal, the former Minjoo Party chief garnered 25.5 percent in approval scores, beating rivals by a wide margin. It was carried out by Realmeter at the request of Maeil Business newspaper.

Support for Ban was mostly divided into Ahn Hee-jung of the Minjoo Party, the governor of South Chungcheong province, and Prime Minister Hwang Kyo-ahn who is serving as acting president.

Ahn's approval rating moved to the second place with 11.2 percent, compared with 6.4 percent tallied a week ago. It was followed by Hwang with 10.5 percent.

As Ahn shares the political support base in the province with the former UN head, Ban's withdrawal helped boost support for the provincial governor.

Prime Minister Hwang also benefited from Ban's drop as there are few contenders found in the conservative bloc to replace the impeached president.

Another survey, which was conducted by the same pollster on the same day at the request of cable news channel JTBC, showed Moon ranking first as the next South Korean leader with 26.1 percent in approval rating.

In this survey, Prime Minister Hwang ranked second with 12.1 percent, trailed by Governor Ahn with 11.1 percent.

Lee Jae-myung of the Minjoo Party, the mayor of Seongnam city to the southeast of Seoul, ranked fourth with 9.9 percent in support scores, while Ahn Cheol-soo of the minor opposition People's Party gained 9.3 percent.