Margolies hails from Montgomery County, as do the two other Democrats in the race, state Sen. Daylin Leach and Dr. Valerie Arkoosh. That likely split the vote there, benefiting Boyle.
Pollster G. Terry Madonna, of Franklin & Marshall College, said Margolies coasted in the race, perhaps counting on the well-known swing vote she cast in 1993 to approve a budget for then-President Bill Clinton. That vote cost her the 13th District seat.
"I think she took it for granted," he said. "I think she assumed there was a preconception that the seat was hers, that they owed it to her because of the vote."
Margolies had support from Clinton and former U.S. Secretary of State Hillary Clinton. Each held a fundraiser for Margolies. Her son, Marc Mezvinsky, is married to Chelsea Clinton.
Boyle also ran unopposed yesterday in the primary for his 170th District state House seat in Northeast Philly.
Republican Carson Dee Adcock, a plumbing-supply-company owner from Abington who lost a bid for the seat in 2010, defeated retired U.S. Air Force Col. Beverly Plosa-Bowser in their primary.
Adcock will face an uphill battle in the 13th District.
Democrats make up 60 percent of the district's registered voters, while Republicans have 28 percent and independent or third-party voters are 12 percent.
The Democratic battle for the 13th District seat frayed into an intraparty financial fracas late in the primary season.
Federal "independent-expenditure" groups spent hundreds of thousands of dollars on campaign commercials, with building-trade unions supporting Boyle while abortion-rights groups opposed him.
Leach filed two Federal Election Commission complaints against Margolies, accusing her of violating regulations on how campaign cash is spent.
On Twitter: @ChrisBrennanDN