Edwards easily won his native South Carolina in Tuesday's primary and Clark, a retired Army general and former NATO commander from Arkansas, triumphed in neighbouring Oklahoma.
Howard Dean earned no wins and perhaps no delegates, his candidacy in peril. Joseph Lieberman was shut out and dropped out of the race to pick a candidate to challenge US President George Bush.
Racking up victories in Missouri, Arizona, North Dakota, New Mexico and Delaware, Kerry suggested that his rivals were regional candidates.
"I compliment John Edwards, but I think you have to run a national campaign, and I think that's what we've shown tonight," the four-term Massachusetts senator said. "You can't cherry-pick the presidency."
With Iowa and New Hampshire already in the bag, Kerry boasts a record of 7-2 in primary season contests, the undisputed front-runner.
A Democratic candidate to run against Bush in November elections will be chosen at the party's national convention this summer by delegates largely allocated in votes around the country in coming months.
"I don't care who wins... I'd get my dog to run. I'm not kidding. I would get Mickey Mouse in there. Anybody but Bush"
An Associated Press analysis showed Kerry winning 65 pledged delegates, Edwards 43, Clark five and Al Sharpton one, with 155 yet to be allocated. Kerry's wins in Missouri and Arizona were the night's biggest prizes, with 129 delegates - nearly half of the 269 at stake.
Tuesday's results pushed Kerry close to 200 delegates out of 2162 needed for the nomination, including the so-called super-delegates of lawmakers and party traditionalists. Dean trailed by nearly 70, Edwards by nearly 100.
Democrats award delegates based on a candidates showing in congressional districts, giving Kerry's rivals a chance to grab a few delegates even in contests they lost.
In nearly every area of the nation, the most diverse group of Democrats yet to cast votes this primary season said they had a singular priority: defeat Bush this fall.
African-American community in
South Carolina account for 30%
"I don't care who wins" the Democratic primary, said Judy Donovan of Tucson, Arizona. "I'd get my dog to run. I'm not kidding. I would get Mickey Mouse in there. Anybody but Bush."
In state after state, exit polls showed Kerry dominated among voters who want a candidate with experience or who could beat Bush.
Dean saved his money for a last stand in Wisconsin on 17 February, a long-shot strategy that some of his own advisers questioned. He ran no television advertisements in the seven states and intended to stay off the air until the Wisconsin vote.
"We're going to have a tough night," Dean told supporters as he promised to keep "going and going and going and going - just like the Energizer bunny."
But Steve Murphy, who ran Representative Dick Gephardt's campaign, said: "Howard Dean is done."
Kerry, who just six weeks ago was written off as a candidate, reshaped the race with victories in Iowa and New Hampshire while Dean's candidacy faltered.
The race turns next to Michigan and Washington state, with a combined delegate total of 204.