The daughter of the South Korea's former military ruler appeared to be leading in Wednesday's presidential vote, putting her on track to become the country's first woman head of state although her narrow advantage meant the race was set to go to the wire.
A win for the 60-year old conservative Park Geun-hye would see her return to the presidential palace where she served as her father's first lady in the 1970s after Park's mother was assassinated by a North Korean-backed gunman.
Exit polls released by three broadcasters showed Park had 50.1 percent of the vote against 48.9 percent for her left-wing challenger, human rights lawyer Moon Jae-in, in a tight race where the predicted outcome was well within the margin of error.
Turnout was 75.5 percent, a touch less than the 77 percent her opponent had appealed for in a bid to turn out the youth vote that was more likely to be for him.
"This makes it difficult to predict the final breakdown of votes and who the winner will be," Woo Jung-yeop, a polling specialist at the Asan Institute for Policy Studies, a Seoul-based think-tank, said of the narrow margin.
If she does win, Park will take office for a mandatory single term in February and will face an immediate challenge from a hostile North Korea and deal with an economy in which annual growth rates have fallen to about 2 percent from an average of 5.5 percent in the past 50 years.
She is unmarried and has no children, saying that her life will be devoted to her country.
At the headquarters of her Saenuri party officials greeted the exit polls with a huge cheer, although a clear picture of results may not emerge until 11 p.m. (1400 GMT).
"I feel good, a 1.2 percent gap on the sampling of 86,000," said Shim Jae-chul, a member of parliament and one of the party's top officials.
The legacy of her father, Park Chung-hee, who ruled South Korea for 18 years and transformed the country from the ruins of the 1950-53 Korean War into an industrial power-house still divides the country.
For many conservatives, he is South Korea's greatest president and the election of his daughter would vindicate his rule. His opponents dub him a "dictator" who trampled on human rights and stifled dissent.
"I trust her. She will save our country," said Park Hye-sook, 67, who voted in an affluent Seoul district, earlier in the day.
"Her father ... rescued the country," said the housewife and grandmother, who is no relation to the candidate.
For younger people, the main concern of the election is the economy and the creation of well-paid jobs in a country where income inequalities have risen in recent years.
Cho Hae-ran, 41, who is married and works at a trading company, believed Moon would raise wages if he won.
"Now a McDonald's hamburger is over 5,000 Korean won ($4.66) so you can't buy a McDonald's burger with your hourly pay. Life is hard already for our two-member family but if there were kids, it would be much tougher."
Park has spent 15 years in politics as a leading legislator in the ruling Saenuri party, although her economic policies remain sketchy.
Park has a "Happiness Promotion Committee" and her campaign was launched as a "National Happiness Campaign", a slogan she has since changed to "A Prepared Woman President".
At times, she has cited former British Prime Minister Margaret Thatcher, a tough proponent of free markets, as her role model. At other times it has been Angela Merkel, the conservative German Chancellor who is Europe's most powerful leader.
NEGOTIATE WITH NORTH
Park has said she would negotiate with Kim Jong-un, the youthful leader of North Korea who recently celebrated a year in office, but wants the South's isolated and impoverished neighbor to give up its nuclear weapons program as a precondition for aid, something Pyongyang has refused to do.
The two Koreas remain technically at war after a armistice ended the Korean conflict and Kim Il Sung, the grandfather of the North's current leader, ordered several assassination attempts on Park's father, one of which resulted in her mother being shot to death in 1974.
Park herself met Kim Jong-un's father, the late leader Kim Jong-il, and declared he was "comfortable to talk to" and he seemed to be someone "who would keep his word".
The North successfully launched a long-range rocket last week in what critics said was a test of technology for an intercontinental ballistic missile and has recently stepped up its attacks on Park, describing her as holding a "grudge" and seeking "confrontation", code for war.
Park remains a firm supporter of South Korea's trade pact with the United States that her opponent has threatened to repeal and looks set to continue the free-market policies of her predecessor, although she has said she will seek to spread wealth more evenly.
Moon had pledged to tackle the power of the country's vast export-oriented industrial conglomerates, the so-called chaebol, but Park has stressed their value in creating jobs.
The biggest of all the chaebol, Samsung Group, which produces the world's top selling smartphone as well as televisions, computer chips and ships, has sales equivalent to about a fifth of South Korea's national output.