He now enters the tough battle for the crucial Pennsylvania contest for the Democratic nomination with a psychological boost that come from winning and lots of guaranteed air time on the national media as the leader.
With over 99 per cent of precincts reporting across Mississippi, Mr Obama led Mrs Clinton by a crushing 60.32 per cent to 37 per cent. His win here has wiped out Mrs Clinton's small 11-delegate gain from her victories in Ohio and Texas last week.
But in a troubling sign that race is strongly affecting voters' choices - despite Mr Obama's attempts to be beyond race - not only did 9 of 10 Black voters support him but Mrs Clinton won more than seven in 10 of the state's white voters.
Blacks comprise 36 per cent of Mississippi's population, the highest proportion in the US.
"It's just another win in our column, and we are getting more delegates," Mr Obama, told CNN from his home in Chicago after spending the day campaigning in Mississippi and Pennsylvania. "I am grateful to the people of Mississippi for the wonderful support. What we've tried to do is steadily make sure that in each state we are making the case about the need for change in this country."
Mrs Clinton also blocked inroads he has made into her white voter base in northern states. Mrs Clinton won narrowly among white independents, who made up 14 per cent of the total electorate. Republicans who decided to cross over for Mrs Clinton - 11 per cent of the vote are now her strongest single group, handing her 85 per cent of their votes. Republicans and independents have been attracted to Mr Obama's campaign, but not in racially polarised Mississippi.
The victory has removed the sheen from Mrs Clinton's dramatic comeback as the campaign moves to the crucial Pennsylvania contest for the Democratic nomination in six weeks' time. Expecting defeat, Mrs Clinton has not campaigned in Mississippi since last week.
Mr Obama also slapped down talk from the Clinton camp that he would make a great vice-presidential running mate.
"With all due respect, I've won twice as many states as Senator Clinton," he said before the vote, calling her tactics a blatant attempt to "okeydoke, bamboozle and hoodwink" voters into supporting her for the presidency. No less a figure than the speaker of the house Nancy Pelosi has said such a ticket is now impossible since the Clinton camp have already ruled out Barack Obama as being suitable commander in chief material.
But among Democrats who left the polls yesterday, six in 10 Obama supporters said he should pick Mrs Clinton for his vice president, if he wins the nomination. Some four in 10 Clinton supporters want her to pick Mr Obama if she wins. In a CNN interview last night Mr Obama diplomatically dodged the question saying merely that Mrs Clinton "would be on anybody's short-list."
Huge crowds turned out to see Mr Obama speak in the state capital Jackson. At Buck's diner yesterday morning he ordered a Southern breakfast of eggs, sausage, toast and grits as he chatted with early morning voters. "You all keep me in your prayers, now," he said, promising to return to the impoverished Delta if he is elected to the White House.
The Illinois senator's strategy has been to target small states like this one that typically vote Republican in presidential elections. But there are only 33 delegates at stake in Mississippi, which has not voted Democrat since Jimmy Carter's election to the White House in 1976, and any bump he gets will be tiny.
As voters went to the polls yesterday both Hillary Clinton and Mr Obama had already moved on to campaign in Pennsylvania where 158 delegates are at stake in what is set to be a much tougher and drawn-out battle. But the trick the candidates need to pull off in the coming 41 days is to persuade wavering superdelegates – the Democratic Party members who hold the casting vote at the August nominating convention – to declare their support.
Mr Obama has been using an aggressive new tone against his rival in Mississippi putting to one side his "kumbayah" style of avoiding negative politicking. He attacked her as part of the old corrupt Washington establishment, telling a huge rally in Jackson that they did not need "the same old folks doing the same old things, talking the same old stuff".
He accused Mrs Clinton and her campaign of duplicity and dirty tricks, saying they leaked a photograph of him in a traditional Somali turban and tribal dress that was "straight out of the Republican playbook". He added: "That's not real change."
The Obama campaign also attacked remarks by Geraldine Ferraro, a Clinton supporter, saying they were "outrageous and offensive". Ms Ferraro had said that the US and the "sexist media" had been caught up with the Obama campaign. "If Obama was a white man, he would not be in this position," she said. "And if he was a woman of any colour he would not be in this position. He happens to be very lucky to be who he is. And the country is caught up in the concept."
Ms Ferraro ran unsuccessfully with Walter Mondale in the 1984 race for the White House. Although she is a fund-raiser and on the finance committee of the Clinton campaign, her remarks were disavowed yesterday. "We disagree with her," a campaign official said curtly.
A little later Ms Ferraro was at it again saying "I really think they're attacking me because I'm white."
Whether authorised of not by the Clinton campaign, Ms Ferraro's remarks have caused race to bubble up again - and send a message directed straight at the large white working class electorate that Mrs Clinton is appealing to in Pennsylvania.
The stalemate in the race for the nomination has turned attention to the disputed contests in Michigan and Florida. Mrs Clinton won both races at the end of January, but the Democratic national committee stripped the states of their delegates because they broke party rules by moving up the date of the contests ahead of Super Tuesday.
The prospect of two important states having no voice in picking the Democratic nominee fills party officials with dread. Although Mr Obama says he wants a compromise that will allow the delegates to be seated - is a way that is not unfair to either candidate - there is no sign of a solution to date.
The latest plan is for a new postal ballot that would enable voters to have their say once again. But a short-notice postal ballot is fraught with difficulty because of the danger of voting fraud and the cost of organising the vote.
In addition, the Obama campaign does not want to run two new contests in states which are likely to go to Mrs Clinton. "The Democratic Party is going to run a mail-in election and they're going to police it … I think it's a nightmare," a senior Obama strategist, David Axelrod, said this week. He pointed out that Oregon took 10 years to develop a fraud-proof statewide postal election.
"Does anyone really believe we're going to get this right? And does anyone really want another screwed-up election in Florida?" said Allan Katz, a member of the Democratic National Committee and Obama supporter.
For the Republican side, there was no real contest and Arizona senator John McCain of Arizona has already clinched his party's nomination.
For rolling comment on the US election visit: independent.co.uk/campaign08
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