But despite her victory, the dynamics of the race are the same as they've been for more than two months. Obama remains the front-runner, and that gets more important the closer the campaign comes to the end of the primary season.
"He's content to essentially run out the clock with his narrow lead, while she needs something dramatic to happen," said California-based Democratic consultant Dan Newman. "A one-run advantage in the first inning isn't a big deal, but a one-run lead in the ninth looms large."
Clinton now faces a dwindling number of contests, and she's at a steep financial disadvantage.
Obama already is spending twice as much on ads airing in North Carolina and Indiana, the two states that come up next, with primaries on May 6. He's even advertising in Oregon, a state that he should win, where voting by mail begins in the first week of May.
Obama can afford to shower every contest with campaign dollars from the $42 million he had at the beginning of April, while Clinton is in debt. She'll have to either persuade donors to give her more money to sustain her long-shot bid or float herself another multimillion-dollar loan.
Then she'll face the uphill battle of convincing the party's elected officials and leaders - the superdelegates - to reject the front-runner Obama in favor of her.
"She has to convince superdelegates that her survival as a candidate doesn't come at the cost of jeopardizing the long-term survival of the party in the fall and in the future," said Democratic consultant Jenny Backus. "And that is a tough argument to make."
In Pennsylvania, Clinton won with the support of whites, women and older voters, according to exit polls conducted for The Associated Press and the television networks.
Underscoring the race's excitement, more than one in 10 voters Tuesday had registered with the state's Democratic party since the beginning of the year. And about six in 10 of them were voting for Obama.
Some voters had a hard time making up their minds. About a quarter of the day's voters reported having decided within the past week, and about six in 10 of them backed Clinton.
She found reason for optimism in the victory that came even though Obama outspent her 3-to-1 in the state.
"He broke every spending record in this state trying to knock us out of this race," Clinton told her cheering supporters. "Well, the people of Pennsylvania had other ideas tonight."
But Clinton also went into Pennsylvania with a big advantage - the demographics matched her strengths and she started with a steep lead in the polls. She won't have that kind of advantage in the coming contests.
Of the states left, the biggest prize is North Carolina, a state that both sides are predicting Obama will win. Clinton dispatched one of her top state organizers, California and Texas veteran Ace Smith, to North Carolina in an effort to get every vote she can. Smith told reporters last week that getting the percentage spread within single digits would be a victory for Clinton. Obama's also expected to win Oregon and South Dakota.
So where can she look for victory? West Virginia and Kentucky are likely Clinton wins, but they offer fewer than 100 delegates combined. She also has a chance in Guam, Puerto Rico, Montana and Indiana. But none of them is likely to give her a big enough margin to put her over Obama.
To win, she needs to convince voters that Obama is not electable in November even though he's ahead in the delegate race.
She needs a big influx of cash.
She needs a stunning change of fortune.
---
EDITOR'S NOTE - Nedra Pickler covers the Democratic presidential
campaign for The Associated Press.
