Hillary Clinton beat rival Barack Obama in Pennsylvania on Tuesday, prolonging an increasingly negative Democratic presidential race and keeping alive her slim White House hopes.
Clinton led 55 per cent to 45 per cent with more than 85 per cent of the vote counted, a strong showing but probably not enough to dramatically change the race or narrow Obama's lead in delegates who select the Democratic nominee at the August convention.
The New York senator survived a heavy advertising onslaught by Obama, who outspent her by more than 2-to-1 in the first Democratic nominating contest in six weeks.
"Some people counted me out and said to drop out, but the American people don't quit and they deserve a president who doesn't quit either," Clinton told cheering and chanting supporters in Philadelphia.
Clinton, whose campaign is in debt and running low on cash, urged backers to visit her Web site and donate.
"The future of this campaign is in your hands," said Clinton, who was joined on stage by her husband, former President Bill Clinton, and daughter Chelsea.
The contest in Pennsylvania, where 158 delegates were at stake, opened the final phase of the Democratic duel for the right to face Republican John McCain in November's presidential election. Nine more contests are scheduled before the voting ends on June 3.
The race moves on to contests on May 6 in North Carolina, where Obama is favored, and Indiana, where the race is more of a toss-up. Obama already was looking beyond Pennsylvania, leaving the state for an evening rally in Indiana.
It was at least the fourth time in the four-month primary battle that Clinton triumphed in potential do-or-die contests. She held off a late charge in the state by Obama, who narrowed a once 20-point lead for Clinton in opinion polls.
"There were a lot of folks who didn't think we could make this a close race when it started," Obama told a rally in Evansville, Indiana.
"Six weeks later, we closed the gap. We rallied people of every age and race and background to our cause," he said. "And whether they were inspired for the first time or for the first time in a long time, we registered a record number of voters who will lead our party to victory in November."
Turnout was heavy at many polling places, and a record number of Pennsylvanians had registered to vote.
Following Clinton's popular vote victories in Ohio, California, New Jersey and Texas, the result added fuel to her argument she is the Democrat who can capture the big and diverse states where the party will need to do well in November.
Exit polls showed the two candidates retained their familiar voter bases. Obama, an Illinois senator who would be the first black US president, won 9 of every 10 black voters and led among young and male voters.
Clinton, who would be the first woman U.S. president, was the choice of more than 60 per cent of elderly voters and more than half of women, exit polls showed.
Clinton wins late deciders
She also won 58 per cent of those who decided in the last week, when Obama was on the defensive over a series of campaign controversies in a debate and Clinton questioned his toughness in an ad featuring images of al Qaeda leader Osama bin Laden.
Obama has a nearly insurmountable lead in popular votes won during the first three months of the primary battle and in delegates. But neither can clinch the nomination without the help of superdelegates -- nearly 800 party insiders who are free to support either candidate.
Clinton hopes her win ignites a strong run through the last nine contests that brings her closer in delegates won and votes cast and convinces superdelegates she is the candidate who can capture the big states that will be crucial in November.
But many Democratic strategists and independent analysts said she needed a bigger rout of Obama in Pennsylvania to fundamentally change a race where he has more money and has won more contests, votes and delegates.
"Clinton wins is the headline. But the second day story is: did she win by enough to change the structure of the race? And I think the answer to that will be no," said Cal Jillson, an analyst at Southern Methodist University in Dallas.
Democratic rules allow the losers in each state to win a proportional amount of delegates, giving Obama big chunks of delegates even when he loses. That means Clinton must win many of the nine remaining contests by big margins to have a shot at significantly closing the gap with Obama in the delegate race.
An MSNBC count gave Obama 1,653 delegates to Clinton's 1,513 before Tuesday's voting in Pennsylvania, well short of the 2,024 needed to clinch the nomination. The delegate apportionment from the state was still unclear.
(Additional reporting by Jeff Mason and Caren Bohan; Editing by David Wiessler)