Yeo, a former labor activist, beat Kang Ki-youn of the LKP. while Jeong, a former prosecutor, won a victory against Yang Moon-seok of the ruling party.

Liberal politicians have received strong voter support in Changwon, as liberal candidates have been selected in three of the four general elections since 2004. Conservative contenders have held firm in Tongyeong on the southeast coast.

The DP and the LKP are expected to fight fiercely to take the initiative ahead of next year's election.

In the by-elections, the DP failed to add a parliamentary seat to its current 128 posts. But it could get the Justice Party's backing in its drive to pass a set of reform bills in the third year of Moon Jae-in's presidency.

The DP clinched an overwhelming victory in the local elections last June, aided by strong support for Moon and his drive for peace with North Korea.

But the public support rating for Moon and the DP has declined, dented by the economic downturn and stalled denuclearization talks between the United States and the North.

Ahead of next year's general elections, the ruling party was able to gauge voter sentiment in the province, a manufacturing hub for the auto and shipbuilding industries that is bearing the brunt of an economic slowdown.

For the conservative LKP, the elections were widely viewed as a test for the leadership of its new chairman, Hwang Kyo-ahn.

The party saw the by-elections as a chance to cement its status as the main opposition party able to deter the DP's liberal agenda.

The conservative party suffered a crushing defeat in last year's local elections as it was still reeling from the fallout of the ousting of scandal-ridden former President Park Geun-hye.

But the support rate for the LKP has recently rebounded to the 30-percent mark for the first time since the corruption scandal involving Park rattled the nation in late 2016.
    
The party is expected to continue to denounce what it calls the liberal government's economic policy failure to muster conservative votes. (Yonhap)