The Boston Globe poll released Friday is the first to give Republican Charlie Baker a lead over Attorney General Martha Coakley. While 37 percent of respondents said they plan to vote for Coakley, 38 percent picked Baker.
A Globe poll earlier this month gave Coakley a lead of 7 percentage points.
Coakley faces two opponents in the Sept. 9 Democratic primary, where she has an overwhelming lead.
Baker, the former president and CEO of Harvard Pilgrim Health Care, served in the cabinets of Republican governors in the 1990s. He lost the governor's race in 2010 to the incumbent, Deval Patrick, and the only elective office he has held is Swampscott selectman.
Coakley, who was elected attorney general in 2006, lost a special election in 2010 for the U.S. Senate seat left vacant by the death of Edward Kennedy. She was defeated by Scott Brown, who became the first Republican to win a Senate race in Massachusetts in 40 years.
This month, a SuperPAC linked to the Republican Governors Association began running ads in Massachusetts touting Baker's experience in state government and business.
The Globe interviewed 605 likely voters from Aug. 17 to Aug. 19 and Aug. 24 to Aug. 26. The margin of error is 4 points.