"Thank you, South Carolina," McCain said to chants of "Mac is Back" from supporters in Charleston. "You know, it took us a while, but what's eight years among friends?"
Joined onstage by his wife, Cindy, and his 95-year-old mother, Roberta, McCain thanked members of the state's Republican establishment, including Sen. Lindsey Graham, who were instrumental in his victory.
"For the last 28 years, the winner of the South Carolina primary has been the nominee of our party," said McCain, 71, who predicted that he would win Florida and be on his way to the nomination.
McCain redeemed himself in South Carolina, a state he lost eight years ago. He is positioned to become the favorite for the Republican nomination if he can win a four-way primary in Florida a week from Tuesday.
Mike Huckabee of Arkansas finished second in the first Southern contest despite an appeal to regional pride. Turnout by evangelical Christians was heavy, but their votes were split among several contenders.
In Nevada's caucuses, Clinton parlayed strong backing from women, Hispanics and older voters into a second straight win over Barack Obama, whose labor union supporters failed to deliver their members in large numbers.
Mitt Romney, the only major Republican contender to compete in Nevada, finished first in his party's caucuses.
"I guess this is how the West was won," Clinton, her voice raw from nonstop campaigning, told boisterous supporters in Las Vegas.
Clinton received the most precinct delegates at stake yesterday, but Obama claimed 13 national convention delegates to Clinton's 12. The actual selection of national delegates will take place at the state's Democratic convention in April.
The near-even split underscored the growing importance of delegate rules as the Democratic race becomes a two-person contest. Clinton and Obama have potent funding bases, making it likely that the campaign will extend beyond Super Tuesday to states such as Maryland, on Feb. 12, and for weeks after that.
Obama is favored to win the next Democratic primary, on Jan. 26 in South Carolina, where blacks are expected to account for half of the vote. The two parties are on separate tracks because of national party rules governing the primary calendar.
Nevada was the first test of strength among Latinos, a key Democratic constituency. According to an Election Day poll of voters as they entered caucus sites, Clinton outpolled Obama by a ratio of more than 2-to-1 among Hispanics, a lopsided advantage that could be crucial in future primaries.
John Edwards' distant third-place finish in Nevada could weaken his hold on white voters in South Carolina, his native state and the only primary he won four years ago. A shift of white voters from Edwards to Clinton could improve her chances of winning Saturday.
Clinton needs heavy support from white voters to offset Obama's expected advantage among blacks. In Nevada yesterday, he defeated Clinton among African-Americans by a 6-to-1 ratio, according to the entrance poll.
But Clinton carried white voters by a 52-34 margin. Almost three of five caucus-goers were women, and Clinton won a majority of their votes. Significantly, Clinton neutralized Obama's advantage among caucus-goers from union households.
Obama had the active support of the Culinary Workers Union, the state's largest. Nine of the state's caucuses were held at casinos where some of the union members work.
The entrance poll did not include voters from those locations. But among those surveyed at other caucus sites, Clinton and Obama evenly split the votes of the roughly 30 percent of caucus-goers from union households.
Former President Bill Clinton, who campaigned aggressively for his wife in the state last week, courted members of the Culinary Workers Union at the Bellagio Hotel and Casino on Friday and reported that many were planning to ignore their union's candidate.
When the caucus votes were counted, Clinton won at seven of the nine caucus sites.
Those results, in heavily unionized Nevada, were likely to again call into question the ability of organized labor to deliver on behalf of its endorsed candidates.
A relative lack of enthusiasm among younger voters also cost Obama. He did better than Clinton among voters younger than 45, but they made up 32 percent of the caucus vote, compared with 40 percent in Iowa, which he won.
More than one-third of the Nevada voters were older than 60, and Clinton beat Obama by a 2-to-1 ratio in that age group.
Among Republicans in Nevada, which has the nation's fourth-highest percentage of Mormons, almost half of Romney's votes came from fellow Mormons, according to the entrance poll.
Ron Paul, the only Republican to run TV ads in the state, was a distant second, narrowly edging out McCain. Duncan Hunter, a California congressman, quit the Republican race last night after finishing seventh in Nevada.
In South Carolina, where Romney outspent his rivals on TV ads, he finished a distant fourth behind Fred Thompson, who sounded a valedictory note after a poor finish that might have ended his candidacy.
McCain won with backing from military veterans, senior citizens and those who said Iraq and terrorism were top concerns, according to an Election Day survey of voters as they left polling places.
The survey found that the economy was the most important issue for voters in South Carolina, which has the fourth-highest unemployment rate in the country.
Illegal immigration was the most important issue for one in four primary voters, and Huckabee won more of their votes than any other candidate.
More than half of South Carolina Republicans said they favor deporting illegal immigrants rather than providing them a path to citizenship or temporary-worker permits. Those voters favored Huckabee, who has taken a tougher anti-immigrant line in recent weeks.
McCain did best among independents, who cast a much smaller portion of the primary vote than they did eight years ago. He and Huckabee split self-identified Republicans.
Voters who described themselves as evangelical or born-again Christians cast more than half of the primary votes. They favored Huckabee over McCain by a 41-27 margin, a smaller advantage than Huckabee had in winning Iowa this month.
Thompson took 15 percent of the evangelical vote, which might have hurt Huckabee.
The former Tennessee senator spoke in the past tense about his campaign last night in somewhat rambling remarks to supporters, but he did not disclose his plans.
Heading into the Republican primary in the state, McCain predicted that "South Carolina will most likely determine who the nominee is."
Last night, Huckabee complimented McCain on running a "civil and good and decent campaign." But in conceding, he told supporters that "the process is far, far, far from over."
Thompson, a former senator from Tennessee, made what might have been his last stand in South Carolina, with in-person campaigning and an intensive TV ad drive over the past two weeks.
Nationally, his campaign has failed to get off the ground, confounding supporters who thought he would become the candidate of the conservative base, which has been searching for a new hero. His inability to meet expectations was blamed on a low-energy personal effort and a flawed strategy that called for him to succeed without an intensive in-person campaign effort.
Thompson, who revealed early last year that he was suffering from a form of cancer, tried to substitute appearances on radio and TV talk shows for the grind of meeting voters in early states such as Iowa and New Hampshire.
Another Republican whose candidacy has been sinking, Rudolph W. Giuliani, will face his moment of truth in the next primary, in nine days in Florida.
Giuliani, running far behind in South Carolina, retreated to Florida after dismal showings in the early states. For most of the past year, he has been the leader in the national polls, but his popularity plunged as he campaigned in places such as New Hampshire and voters started making up their minds.
The former New York mayor has lost half of his national support among Republican voters over the past two months, polls have found, and he has fallen to fourth in the Republican field, according to the most recent national poll by CNN/OpinionResearch, which was completed Thursday.
Despite spending more than $50 million, Giuliani has yet to win a convention delegate, according to the latest count by the Associated Press. If he loses to McCain in Florida, it could effectively end the New Yorker's chances.
McCain was slightly ahead in Florida polling conducted before his South Carolina victory. Giuliani, if he upsets McCain in Florida, will become a serious contender again, just as the race heads into the big round of primaries and caucuses Feb. 5, when 21 states hold contests.
Several of the biggest delegate prizes that day are in winner-take-all New York, New Jersey and Connecticut, where Giuliani could do well.
Democrats (98% of polls reporting)
x-Hillary Clinton: 51 percent
Barack Obama: 45 percent
John Edwards: 4 percent
Republicans (93% of polls reporting)
x-John McCain: 33 percent
Mike Huckabee: 30 percent
Fred Thompson: 16 percent
Mitt Romney: 15 percent