The new poll comes after a barrage of attack ads from the Corbett camp.
Magellan's findings were in line with a New York Times/CBS poll last week that found Wolf holding a nine-point lead. That survey was conducted via the Internet over 21 days, however, a method many pollsters say is problematic, in part because it excludes people who are not online.
Magellan, a Republican firm based in Colorado and Louisiana, used automated telephone responses from 1,214 Pennsylvanians who said they were registered voters and were likely to cast ballots in November.
The respondents were contacted on July 29 and 30. Results are subject to a potential margin of error of just under 3 percentage points.
Political races often tighten as fall approaches, and the Wolf campaign has said it expects a closer race than earlier polls suggested.
According to Magellan, 43 percent of respondents in the latest poll said they were registered Republicans; 46 percent said they were Democrats; and 10 percent identified themselves as independent.
Democrats have a wider registration edge overall in Pennsylvania. About 50 percent of the state's 8.2 million voters are Democrats, compared with 37 percent for the GOP. But the electorate in a midterm election such as this year's generally skews more Republican than in presidential years.
In the 2010 governor's race between Corbett and Democrat Dan Onorato, the exit poll conducted for the TV networks found 40 percent of those voting were registered Democrats, to 37 percent Republican - a three-point spread, just as in the Magellan poll.