Clinton's 10-point victory margin in the 'keystone state' had narrowed from 20 points in opinion polls before the start of the campaign, but was sufficient to ensure the hard-fought Democratic race will keep going, possibly up to the party convention in August.
With 95% of votes counted, she had 55% to Obama's 45%, as women and working class whites gave their support to the New York senator. She gained strong margins among gun-owners, church-goers, and rural residents, while blacks and educated white city-dwellers backed Obama.
Analysts say that although the margin was significant in a state she was always bound to win, it was not sufficient to turn the race around. Obama remains ahead in overall votes and numbers of delegates after four months of primaries, and has far more campaign money to spend than Clinton.
Obama is likely to win the North Carolina contest next month, but the race remains wide open in Indiana, where the Illinois senator gave a rally speech on Tuesday evening.
Clinton seized international headlines during the Pennsylvania campaign with her aggressive rhetoric on Iran.
When asked on national TV how she would respond to an Iranian nuclear attack against Israel, she said: "I want the Iranians to know that if I'm the president, we will attack Iran... we would be able to totally obliterate them."
Obama said in response: "Using words like obliterate - it doesn't actually produce good results, and so I'm not interested in saber-rattling."
Many voters said the campaign debates had been marred by negativity, and around two-thirds of Pennsylvanians believed Clinton's attacks against her rival had been unfair.
Although Obama has gained an almost unassailable lead in terms of popular votes, it is becoming increasingly clear that neither candidate has any hope of securing their nomination without the backing of 'superdelegates' - governors, congressmen and party elders who can go with or against the popular vote.
About 90% of Pennsylvanians polled during the campaign said they considered the economy to be the most important issue for the election, and believed that the United States has already entered a recession.
