South Korea's conservative ruling party prevailed in the tightly contested parliamentary elections Wednesday, a windfall for the beleaguered party trudging towards the December presidential election.

With almost all votes counted early Thursday, President Lee Myung-bak's Saenuri Party appeared to have won 152 seats in an upset victory, retaining its parliamentary majority, according to the National Election Commission.

The main opposition Democratic United Party garnered 127 seats, losing the battle it framed as a referendum on the Lee government. The center-left party, however, emerged decisively victorious in Seoul.

The minor opposition Unified Progressive Party, which fielded joint candidates with the Democrats, gained 13 seats.

Of some 42 million eligible voters, 54.3 percent cast their ballots. Of 300 seats up for grabs, 246 were elected directly and 54 divided among parties based on proportional representation.

The opposition once looked set to take over the parliament, as a series of scandals involving ruling party members and key officials in the Lee administration, coupled with the lackluster domestic economy, hit hard the conservative camp.

The Saenuri Party also made decisions unpopular among the disenchanted young voters: It led the railroading of a controversial trade agreement with the United States, and is pressing ahead with the construction of a naval base in a southern resort island despite mounting criticism.

Most recently, allegations surfaced government officials illegally spied on civilians, a claim that shook the ruling camp just weeks before the general elections.

Mishaps of the conservatives had proven to be a boon for the liberals, who managed to form broad alliances that galvanized the usually divisive liberal and progressive political forces prior to the polls.

It was a short-lived boon, however, as the liberals struggled with infighting and failed to extinguish a controversy involving one of its candidates whose lewd remarks from the past came back to haunt him.

"We have made excruciating efforts to arrive at this result," Lee Hye-hoon, the chief campaign manager of the Saenuri Party, said in a statement. "Regardless of the poll result, our reform efforts will not stop."

The Democratic United Party said it has failed to give voice to those frustrated with the ruling camp's mismanagement of state affairs and corruption.

"We're sorry to have disappointed you," chief campaign planner Park Sun-sook said during a briefing late Wednesday. "But I do not believe the poll results suggest the people have approved business-friendly policies and corruption-ridden politics by the president and his party."

The general elections, meanwhile, offered a glimpse into the presidential race later this year, with the Saenuri Party's triumph providing tailwind for its leader Park Geun-hye, a presidential aspirant.

Still, Moon Jae-in of the Democratic United Party remains a potent rival with his symbolic victory in a district in Busan, a conservative bastion.

Chung Sye-kyun, another liberal heavyweight and presidential hopeful, further raised his national profile by winning the politically important Jongno district in central Seoul.