By contrast, the race has tightened further in national polls and in some battleground states - notably Ohio - reflecting a surge in support for Romney after the debate.
"Our poll, and the vast majority of polling in Pennsylvania, shows a structural lead for the president which has held up," said pollster Jeffrey Plaut, a partner in the Global Strategy Group, the Democratic firm in The Inquirer poll. "That lead is buttressed and framed by a very significant gender gap," he said.
Obama leads among women, 55 to 37 percent, the poll found, while Romney holds a 48 to 43 percent edge among men.
"As a campaign pollster, I wouldn't take great comfort from these numbers if I were advising Obama," said Plaut's Republican counterpart, Adam Geller of National Research Inc. "When you're an incumbent at 50 percent, you're treading water, and we know that most undecideds break to the challenger."
In addition, he said, young voters who favor Obama don't show the same levels of enthusiasm they did four years ago.
The latest poll is based on live telephone interviews conducted from Oct. 4 through Oct. 8 with 600 voters across Pennsylvania who say they are certain or likely to cast ballots. The results are subject to a margin of error of plus or minus 4 percentage points. The first presidential debate, which drew a television audience of about 70 million, was held on Oct. 3.
The findings come on the eve of Thursday night's debate between Vice President Biden and Romney's running mate, Rep Paul Ryan.
Across the Delaware River, The Inquirer New Jersey Poll found that Obama holds an 11-point lead over Romney, an uptick of 3 points for Romney in the Garden State over the last month.
In addition to women, the new Pennsylvania poll finds Obama running strongest among young voters, those over 65, and those with a college education. Geographically, the president leads by 27 points in the five-county area that includes Philadelphia and its suburbs: 58 percent to 31 percent for Romney.
More than three-quarters of likely Pennsylvania voters said they watched at least part of the first debate in Denver; 43 percent said they saw all of it. And 84 percent of likely voters statewide say they saw news coverage of the debate and reactions to it.
Republicans in the state are more intensely interested in the race (74 percent) than Democrats (65 percent) or independents (68 percent) - a measure of supporter enthusiasm that the pollsters said could benefit Romney.
Those who watched at least some of the debate or saw news coverage judged Romney the winner by a margin of 65 percent to 15 percent. Even a majority of Democrats in that group (52 percent) said Romney won; just 22 percent called Obama the victor.
Thirty-six percent of those who watched the debate or followed it in the news said they are now more likely to vote for Romney, compared with 30 percent who said they are less likely to back him. Conversely, 24 percent said they are more likely to vote for Obama as a result, while 33 percent are less likely.
On some of the debate's topics, 52 percent said Obama would be best at addressing education (to 33 percent who chose Romney); likely voters also preferred Obama, 49 percent to 36 percent, on Medicare. The health insurance system for seniors has emerged as a flash point in the campaign, with both Romney and Ryan saying the program needs to be revamped to involve competition from private insurers.
Obama also had a narrow edge on the issue of taxes, with 45 percent saying he would be better on the issue, to 43 percent for Romney.
Respondents favored Romney on jobs and the economy, 47 percent to 43 percent, and resoundingly said he would do best at handling the federal deficit - by a margin of 48 percent to 38 percent.
"Mr. Obama is spending like a drunken fool," said poll respondent John Plowright, a Republican in Glen Mills, Delaware County, who said he is voting for Romney primarily on that issue. "We have a $16 trillion national debt. How long can that go on?"
The poll comes as the Romney campaign has shifted some of its paid field staff from Pennsylvania to Ohio, where early voting has begun. Campaign officials said Romney's strategists remain committed to competing here, noting that only five of 64 staffers were sent to Ohio, and that the Keystone State does not have early balloting.
And yet neither Romney nor Obama is advertising on Pennsylvania broadcast TV, the most expensive and serious marker a campaign can put down on a state. Some national cable TV ads are visible to voters here.
Several state Republicans who have been briefed on the Romney campaign's plans say it is closely watching its own polling and other surveys to see whether the race tightens, and will put ad money into the state if it sees an opportunity here.
Meanwhile, at least $9 million has been invested in the GOP ground game in Pennsylvania, called Victory, a joint effort of the Romney campaign and the Republican National Committee. Victory staff and volunteers have made 3.5 million voter "contacts," officials said, including four times more phone calls and 37 times more door-knocks than by the same time in the 2008 race. Volunteers in Bucks County knocked on 19,000 doors last weekend.
"With his strong debate performance and the momentum that has followed, Romney has positioned himself as an acceptable alternative to the president - after five months of being painted as unacceptable," said Alan Novak, a GOP strategist and former chairman of the state party.
"If the momentum continues," he said, "I don't think Pennsylvania is off the boards."
About the Polls
The Inquirer Pennsylvania and New Jersey Poll results are based on telephone interviews conducted Oct. 4 through Oct. 8 with 600 likely presidential-election voters in Pennsylvania and 604 in New Jersey.
Polls were conducted by a bipartisan team of national political pollsters - Jeffrey Plaut, founding partner of the Democratic firm Global Strategy Group, and Adam Geller, chief executive of the Republican firm National Research.
The estimated margin of error for statewide results is plus or minus 4 percentage points; for results for the five-county area - Bucks, Chester, Delaware, Montgomery, and Philadelphia counties - the margin is plus or minus 6.9 percentage points. The Pennsylvania Poll is sponsored by Susquehanna Bank.
Results for the seven-county South Jersey area - Atlantic, Burlington, Camden, Cape May, Cumberland, Gloucester and Salem counties - have a margin of error of plus or minus 8.5 percentage points. The New Jersey Poll is sponsored by PSEG.
Contact Thomas Fitzgerald at 215-854-2718 or email@example.com, or follow @tomfitzgerald on Twitter. Read his blog, "The Big Tent," at www.philly.com/BigTent.