Barack Obama routed Hillary Rodham Clinton in a racially-charged South Carolina primary, regaining much-needed campaign momentum with the help of black voters in the prelude to next month's coast-to-coast presidential nomination competition in which nearly half the US states will vote.
Former Sen John Edwards, who has yet to win any of the early state contests, finished third Saturday, a sharp setback in his native state where he triumphed in his 2004 vice presidential campaign.
Landslide margins among black voters fueled Obama to his win, allowing him to overcome the edge that Clinton and Edwards had among whites in the first Southern state where the Democrats competed. The turnout of more than a half-million voters was a new record for the state party.
South Carolina's Democratic race was particularly significant for Obama, who is aiming to become the country's first black president, because it was the first contest in which blacks were expected to be a large factor in the outcome.
Blacks accounted for about half of the voters, according to polling place interviews, and four out of five supported Obama. Black women turned out in particularly large numbers. Obama, the first-term Illinois senator, got a quarter of the white vote while Clinton and Edwards split the rest.
"The choice in this election is not about regions or religions or genders," Obama said at a boisterous victory rally. "It's not about rich versus poor, young versus old and it's not about black versus white. It's about the past versus the future."
The audience had chanted "Race doesn't matter" while they awaited Obama's appearance.
Clinton issued a statement saying she had called Obama to congratulate him on his victory.
Nearly complete returns showed Obama winning 55 per cent of the vote, Clinton gaining 27 percent. Edwards had 18 per cent and won only his home county of Oconee.
Obama also gained 25 convention delegates, Clinton won 12 and Edwards eight.
The victory was Obama's first since he won the kick-off Iowa caucuses on January 3. Clinton, a New York senator and former first lady, scored an upset in the New Hampshire primary a few days later. They split the Nevada caucuses, she winning the turnout race, he gaining a one-delegate margin.
In a historic race, she hopes to become the first woman president, and Obama is the strongest black contender in history.
The South Carolina primary also marked the end of the first phase of the campaign for the presidential nomination, a series of single-state contests that winnowed the field and conferred co-front-runner status on Clinton and Obama. But, until now, relatively few delegates have been at stake. That all changes on February 5 when 22 of the 50 states hold contests in a virtual nationwide primary dubbed "Super Tuesday."
Clinton flew to Nashville on Saturday as the South Carolina polls closed, and looked ahead. "Now the eyes of the country turn to Tennessee and the other states voting on February 5," she said, adding "millions and millions of Americans are going to have their voices heard."
Edwards said Saturday night that he is forging ahead to the February 5 primaries with a belief that the "dynamic could shift at any time."
Obama took a thinly veiled swipe at Clinton in his remarks at his victory rally.
"We are up against conventional thinking that says your ability to lead as president comes from longevity in Washington or proximity to the White House. But we know that real leadership is about candor, and judgment, and the ability to rally Americans from all walks of life around a common purpose -- a higher purpose," Obama said.
The runup to South Carolina was marked by a week of mud-slinging on the part of Clinton and Obama, with the two candidates exchanging pointed jabs and accusations as Clinton's husband, former President Bill Clinton weighed in on his wife's behalf. That prompted Obama to complain that he felt he was running against two Clintons.
The loss was not entirely unexpected for Clinton, who has led in national polls. Her husband down-played the likelihood of her carrying a state where Obama would carry the support of blacks. Each side accused the other of playing the "race card."
Clinton campaign strategists denied any intentional effort to stir the racial debate. But they said they believe the fallout has had the effect of branding Obama as "the black candidate." By week's end, one poll indicated that Obama's support among whites in the state had dropped sharply.
Obama on Saturday gained an endorsement from Caroline Kennedy, who likened him to her late father, President John F Kennedy, in an opinion piece in The New York Times.
The February 5 races offer more than 1,600 convention delegates for the Democrats while a total of 2,025 delegates are needed to secure the party nomination. South Carolina offers 45.
Meanwhile, the Republicans were focused on Florida, where a primary Tuesday will be their last major contest before the "Super Tuesday" primaries that are little more than a week away. Sen John McCain and former Massachusetts Gov Mitt Romney have been locked in a close fight for the lead in polls.
McCain received a key endorsement on Saturday from Florida's Republican governor, Charlie Crist.
In a heated exchange, McCain accused Romney of wanting to set a timetable to withdraw US troops from Iraq, drawing immediate protest from his rival, who said: "That's simply wrong and it's dishonest, and he should apologise."
In Orlando, Rudy Giuliani, the former New York City mayor who is trailing in polls and trying to climb his way back into the leaders pack, sought to take the high road, saying he wanted to "remain positive".
The state offers the winner a hefty 57 delegates to the Republicans' nominating convention next summer and a shot of energy heading into the February 5 races.
There will be more than 1,000 Republican delegates at stake on February 5, enough to give a candidate a substantial boost toward the 1,191 needed to win the presidential nomination. (AP)
Obama wins South Carolina primary