PHILADELPHIA -- Hillary Clinton vowed Tuesday night she would not drop out of the Democratic nomination fight and thanked her supporters for a hard-fought victory against rival Barack Obama in the Pennsylvania primary.

Video | Results Analysis | Slideshow

Clinton was winning 55 percent of the vote to 45 percent for her rival with 80 percent counted in Pennsylvania at about 11 p.m. EDT.

Her victory, while comfortable, set up another critical test in two weeks time in Indiana. North Carolina votes the same night, with Obama already the clear favorite.

"Some counted me out and said to drop out," the former first lady she said at a Philadelphia rally. "But the American people don't quit. And they deserve a president who doesn't quit, either."

"The tide is turning," Clinton said, while acknowledging that she lags far behind Obama in campaign funds and making an appeal for donations on her Web site.

After walking to the podium to the strains of Tom Petty's "Won't Back Down," Clinton, joined by husband and former President Bill Clinton and their daughter, Chelsea, congratulated Obama on what she called a historic race.

"It's a long road to 1600 Pennsylvania Ave., and it runs right through the heart of Pennsylvania," she said.

The last of the big states to vote, Pennsylvania had 158 delegates at stake, the largest prize remaining in a primary season that ends on June 3.

Obama took comfort in making the primary less than a blowout for Clinton.

Already campaigning in Indiana, the Democratic presidential front-runner told supporters in Evansville on Tuesday night that he was able to narrow the gap in Pennsylvania, register a record number of voters and rally people of all backgrounds to his campaign.

After the bruising contest, Obama said bickering and tit-for-tat politics obscured the great issues of the day -- two wars, a recession and a planet in peril.

The Illinois senator told his Evansville rally that many people didn't think he could make it a close race in Pennsylvania, where Clinton once enjoyed large leads in polls.

Exit polls found that one in 10 voters, half of them former Republicans, changed their party registration to vote in the state's Democratic race. And one in five voters said they decided for whom to vote within the final week of the six-week Pennsylvania campaign. About one in 10 said they made up their mind Tuesday.

The electorate was overwhelmingly white, while a little more than half of voters were women. About three in 10 were age 65 or over. A quarter had household family income of more than $100,000 last year and about as many reported having a postgraduate degree.

Three in 10 Pennsylvania Democratic voters were union members or had one in their household. And four in 10 had a gun owner in their household. About one in five voters said the race of the candidates was among the top factors in their vote. About as many said that about the candidates' gender.

Pennsylvania Democrats had a sour view of the economy. Four in 10 said the country is in a serious recession and at least as many called it a moderate recession. Only about one in 10 said the economy is not in recession. At least half of voters said the economy was the most important issue facing the country. About half as many said Iraq was the top issue. Health care trailed in importance.

With 158 delegates at stake, Pennsylvania offered the largest prize remaining in a primary season that ends on June 3.

Obama began the night with a delegate lead, 1648.5-1509.5, out of 2,025 needed to win the nomination.

Both rivals sought to shape expectations in advance. Obama said he expected to lose, but narrowly, and worked to limit any gains Clinton made in the delegate chase.