Clinton's 10-point win paid immediate dividends in fund-raising for the cash-strapped New York senator and shaved off some of Obama's lead in popular votes and in delegates who select the Democratic nominee at the August convention.
Both candidates immediately looked to the next round of contests on May 6 in North Carolina, where Obama is favoured, and Indiana, which is considered a toss-up.
"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. A campaign spokesman said she raised $2.5 million (1.25 million pounds) in the hours immediately after she won Pennsylvania.
"The future of this campaign is in your hands," Clinton told her supporters. She was joined on stage by her husband, former President Bill Clinton, and daughter Chelsea.
Clinton survived a heavy advertising onslaught in Pennsylvania by Obama, who outspent her by more than 2-to-1 in the first Democratic nominating contest in six weeks. She won with 55 percent of the vote to Obama's 45 percent.
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.
Obama, who narrowed a 20-point Clinton lead in opinion polls before falling short, already was looking ahead. He left Pennsylvania before the polls closed for an evening rally in Indiana.
"There were a lot of folks who didn't think we could make this a close race when it started," Obama said in Evansville. "Six weeks later, we closed the gap. We rallied people of every age and race and background to our cause."
