The Franklin & Marshall College Poll, released Thursday, is the first survey of Pennsylvania voters since the candidates started airing political commercials shortly after the July 4 holiday weekend.
The results don't look good for Corbett, who could become the first incumbent governor in the modern era to lose re-election unless he finds a way to connect with voters before Nov. 4. The F&M poll and other polls were accurate in predicting Wolf would beat three other Democrats in the May primary.
The latest F&M poll shows Wolf, a wealthy York businessman and former state revenue secretary, holding a lead of 25 percentage points over Corbett, the former prosecutor-turned-governor from the Pittsburgh suburbs.
Wolf leads Corbett 49 percentage points to 24 percentage points, the poll shows, compared to 47 to 25 in June. The poll also found one-in-four voters undecided, with slightly more of them leaning toward Wolf.
Corbett's overall approval rating remains historically low at 24 percent, which is 10 percentage points below Democratic President Barack Obama's rating.
Corbett's numbers are not good among his own party, either. Forty percent of Republican voters rated Corbett as doing an "excellent" or "good" job in his first term, which began in January 2011.
Corbett campaign spokesman Chris Pack dismissed the F&M poll because it uses registered voters rather than likely voters. He said the race has tightened, pointing to an internal poll, and to a new type of online polling done in part by the New York Times and CBS News. Both put Wolf's lead below 10 percentage points.
"Regardless, the only poll that will matter is on Election Day, when we are confident Pennsylvanians will re-elect Tom Corbett and [Lt. Gov.] Jim Cawley for a second term," Pack said.
Corbett's approval numbers have not changed this summer despite spending millions of dollars on TV commercials, F&M pollster G. Terry Madonna said.
Meanwhile, Wolf has avoided rookie mistakes and controversy, Madonna said, while Corbett has had to defend his decision to keep controversial former Education Secretary Ron Tomalis on the payroll as an adviser.
"Wolf only has to be an acceptable alterative, not the superior candidate," Madonna said.
Corbett's main public relations problem remains widespread anger over education funding cuts that Corbett imposed in his first budget, 2011-12.
That year, Corbett was mandated by a new law to increase pension payments by $600 million to school employees and state workers to cover decades of back debt to the pension systems.
At the same time, the state was losing $655 million in federal stimulus money that had been used in part to prop up the state education budget during Democratic Gov. Ed Rendell's final two fiscal years. Corbett also cut $355 million in state funding to a popular grant program and charter school reimbursements.
The pension payment increases did not find their way into the classrooms, while the loss of federal funding and state cuts had a direct negative impact on teacher layoffs and program cuts. Corbett also reduced higher education spending by 19 percent.
Education is the top priority for 22 percent of voters, the F&M poll found, followed by taxes at 19 percent.
Wolf's campaign and various special interest groups have been airing commercials criticizing the education cuts. Corbett's commercials, meanwhile, have criticized Wolf as a millionaire who wants to raise income taxes, and have accused him of using Delaware tax laws to lessen taxes for his own business.
Wolf wants to create a graduated personal income tax, which would raise taxes on higher incomes and reduce taxes on lower incomes. He has not provided details.
The F&M poll found 82 percent of respondents had seen commercials for both candidates, but suggests that Corbett's ads have not resonated with voters enough to alter the dynamics of the race.
In a statement, Wolf campaign spokesman Jeffrey Sheridan kept the focus on education.
"Tom Wolf will restore Gov. Corbett's drastic cuts to our schools and invest in our future workforce to build a stronger middle class," Sheridan said.
The poll of 520 registered voters was conducted between Aug. 18 and 25. It has a margin of error of plus or minus 4.3 percentage points.