John Edwards emerged as the principal rival by scoring a convincing win in South Carolina, while General Wesley Clark managed to stay in the race by declaring a wafer-thin victory in Oklahoma.

The election night also claimed victims. Joe Lieberman pulled out of the contest late last night after being thrashed by Senator Kerry in Delaware, the only state he had a hope of winning. "Today the voters have rendered their verdict and I accept it," Mr Lieberman said.

Howard Dean was the other big loser. He had scarcely campaigned in the seven states voting yesterday, mostly because of lack of funds. But his camp had expected to him to perform better than he did, because of his radical appeal and strong state organisations. In the end, he came in a poor third in every state except Oklahoma and South Carolina, where he finished fifth.

Yesterday Mr Dean took his campaign to Washington state, which he hopes to win on Saturday. He promised supporters there to keep "going and going and going and going - just like the Energizer bunny".

The other state voting on Saturday, Michigan, now looks out of Mr Dean's reach, as Senator Kerry has extended his lead in the polls to 40%.

Senator Kerry was also in Washington state last night, arriving in Seattle in triumph, to meet a ballroom full of supporters.

"This is fantastic," he said. "We won from the east coast to the south-west and north-west; and we came in a strong second in South Carolina; and in a close race in Oklahoma."

Senator Kerry claimed he had been outspent by five to one by Gen Clark in Oklahoma and by the same ratio by Senator Edwards in South Carolina.

Kerry aides portrayed Mr Edwards as a regional candidate.

"He only ran in only two states in today's races - South Carolina and Oklahoma - and he's indicating he's only going to run seriously now in Tennessee and Virginia," David Wade, a Kerry spokesman said yesterday.

"John Kerry is going to be a national candidate. If you're going to be president of the United States, you've got to run everywhere."

Senator Kerry won crushing , double-digit, victories in Missouri and Arizona - the two biggest prizes in terms of delegates to the Democratic convention in July - as well as in three smaller states: New Mexico, Delaware and North Dakota.

Senator Edwards' win in South Carolina was just as convincing, however. He beat Mr Kerry by 46% to 30%. The victory and his surprise close second place in Oklahoma, kept him firmly in contention, while denying Mr Kerry the clean sweep that would have effectively ended the race.

Senator Edwards, who was born in South Carolina, portrayed his win as bigger than a local phenomenon.

"I think South Carolina is a great test for winning in the south, winning among rural voters and winning among the African-American voters," he said last night.

Gen Clark's margin in Oklahoma was only 1,200 votes, and had yet to be officially confirmed yesterday. However, he embraced it like the lifeline it was to his campaign.

"I won a state and I'm just thrilled," he declared. He announced he was going to travel to Tennessee and Virginia, which hold primaries next Tuesday, to compete with Senator Edwards for primacy in the south.

Before that, Michigan and Washington state will vote this weekend, testing the ability of the two southerners to compete outside the region. The two races will also be a test of whether there is any life left in the Dean campaign, which looked like an unstoppable juggernaut only a few weeks ago.

In his first serious test among black voters, the only African-American candidate in the race, the Rev Al Sharpton, attracted 18% of black support. But with negligible backing among whites, he barely scored 10%.

Mr Edwards performed best among white moderates, winning 50% of the white vote compared with 28% for Mr Kerry.

African-American voters were evenly split between Mr Edwards (37%) and Mr Kerry (34%) with Mr Sharpton third with 18%.

Mr Kerry's performances last night should quell concerns about his ability to attract minority support, particularly among African Americans who comprise the core of the Democratic base.

Mr Edwards had staked everything on winning in South Carolina, spending more time in the state than any other candidate, with the exception of Mr Sharpton, and insisting he would bow out unless he won.

His campaign made great play of his southern roots; he was born in the state and serves as senator in neighbouring North Carolina. "The south is not George Bush's backyard," said Mr Edwards, who performed best among white moderates. "It's my backyard, and I can beat him in my own backyard." Another important constituency to have emerged during this campaign, particularly for Mr Kerry and Gen Clark, has been Vietnam veterans. Seven in 10 Oklahoma voters, and nearly as many in South Carolina, said they had served in the military or have somebody in their households who did.

Saturday's contests in Michigan and Washington states will be followed by primaries in Tennessee and Virginia next Tuesday. The contest will almost certainly remain competitive until March 2, when delegate-rich California, Georgia, New York and Ohio join six other states on what has become known as Super Tuesday.