PHILADELPHIA, Pennsylvania (CNN) -- U.S. Senator Hillary Clinton edged rival Sen. Barack Obama in the Democratic primary in Pennsylvania, saying victory showed she had the better shot at winning in November than he.

Sen. Hillary Clinton addresses supporters following her win in Pennsylvania.

"It's a long road to 1600 Pennsylvania Avenue and it runs right through the heart of Pennsylvania," she told supporters in Philadelphia Tuesday night.

Her top advisers had called the state a must-win to stay in the race.

"For six weeks, Senator Obama and I have criss-crossed this state -- meeting people up close, being judged side by side, making our best case," she said to cheering supporters. "You listened and today you chose."

Obama congratulated Clinton on her win and said his campaign closed what had been a huge margin in her favor. Watch Obama claim his campaign's own victory

"There were a lot of folks who didn't think we could make this a race when it started," he said at a campaign rally in Evansville, Indiana, where Democrats will go to the polls May 6. "They thought we were going to get blown out. But we worked hard and traveled across the state, to big cities and small towns, to factories and VFW halls and now, six weeks later, we closed that gap."

Obama leads in overall votes, states won and pledged delegates. And unless "the wheels come off his wagon," Obama was likely to hold that lead, said David Gergen, a former adviser to both Republican and Democratic candidates.

With 80 percent of Pennsylvania precincts reporting, Clinton was leading Obama 55 to 45 percent. A total of 158 delegates to the convention were at stake.

Her win adds to those in other big states, like Ohio, New York and California and, according to her campaign, should revive questions about whether Obama can beat presumptive Republican nominee John McCain in November. Watch Clinton's victory speech »

Polls closed at 8 p.m. local time (0000 GMT) after what election officials in Pennsylvania's largest cities called a solid but not record-breaking turnout.

Heading into the primary, Clinton led Obama in published polls by nearly 20 points, but Obama closed the gap to have a competitive showing and outspent her by more than 2-to-1 in the process.

The last week of campaigning included a tough debate between Obama and Clinton, who pounded her rival for his recent remark that decades of economic decline had left some rural voters "bitter" and clinging to religion and guns.

CNN exit polls showed nearly a quarter of state voters made their decisions in the past week, and those voters leaned toward Clinton by a margin of 56 percent to 44 percent.

Weekly churchgoers made up almost 36 percent of the electorate, who went to Clinton by a 56-44 margin. More than a third were gun owners, and they preferred Clinton by an almost-identical margin -- 60 percent to 40 percent, the polls found.

Exit polls showed Obama appeared to rack up wide margins in Philadelphia and its surrounding counties. Clinton supporters turned out heavily in Pittsburgh and the counties of western Pennsylvania, and she racked up similarly lopsided margins in the state's industrial northeast, exit polls found.

Among the state's black voters, who are heavily concentrated around Philadelphia, Obama racked up margins of more than 90 percent. The voting bloc comprised about 14 percent of the vote, while whites made up about 80 percent and voted 60-40 for Clinton.

Early exits polls indicated Obama scored big with new Democratic voters in the state while Clinton fared better with voters who made up their mind in the final days of campaigning. They also indicated the economy was the number one issue.

Analysts said a big win for Clinton could propel her back into the race. With neither candidate expected to gain a simple majority of delegates before August's Democratic Convention, the nomination could be decided among the party's 800 "superdelegates" -- state governors, members of Congress and party leaders and officials -- among whom Clinton continues to hold influence.

"If Clinton wins by more than 10 points, which was her margin in neighboring Ohio and New Jersey, her campaign will have new momentum and she will soldier on," said Bill Schneider, CNN senior political analyst.

"If Clinton wins by single digits, we're in a political twilight zone. Nothing changes." But if Obama scores an upset, Schneider said, "Clinton will face tremendous pressure to end her campaign rather than damage the party."

Obama played down his chances of a surprise victory despite outspending Clinton by about $7 million to her $2.7 million in the state. His hopes rest on a strong performance in Philadelphia where he is expected to do well among African-American voters, among large numbers of newly registered voters and in the city's wealthier suburbs.

Pennsylvania is also holding a Republican primary, but McCain has already secured the 1,191 delegates needed to win his party's presidential nomination. E-mail to a friend

All About Pennsylvania • Hillary Clinton • Barack Obama