Toomey came out ahead, 46-39, in the poll, conducted Aug. 25-28.
McGinty, who served in former President Bill Clinton's administration, held a steady lead in the last four Pennsylvania Senate poll, leading by three points in a Quinnipiac poll from mid-August.
The new Emerson poll shifted TPM's Electoral Scoreboard from favoring McGinty to favoring Toomey.
The poll surveyed 800 likely Pennsylvania voters through an automated survey, including only landline phone numbers. The results have a margin of error of plus or minus 3.4 percent.
TPM's PollTracker Average for the Pennsylvania Senate race shows Toomey leading McGinty, 46.8 to 39.9.