Rep. Heather Sanborn defeated longtime Portland City Councilor Jill Duson in the Democratic primary for an open Senate seat representing part of Maine’s largest city.

With all Portland and Westbrook precincts reporting, Sanborn had 3,078 votes, or 59 percent. Duson had 2,181 votes, or 41 percent.

Duson conceded the District 28 race shortly after 11 p.m., posting on Twitter that “it looks like serving in the State Senate is just not meant to be.”

Sanborn and Duson competed in the Democratic primary to fill a seat being vacated by Mark Dion, who is running for governor. The winner of the primary will be the favorite to win the general election for the District 28 seat, which represents part of Portland and part of Westbrook. It has long been held by Democrats.

Patrick Martin of Westbrook ran unopposed in the Republican primary and will face the Democratic primary winner in November.

Duson and Sanborn both live in Portland, have law backgrounds and have similar positions on issues such as Medicaid expansion, school funding and gun control. But they differed in their experience and how they would approach their new role as state senator.

Sanborn, co-owner of Rising Tide Brewing Co., is completing her first term as a state representative and wants to make the move to the Senate, which she described as a “smaller, more deliberative body” where she can lead on health care and clean energy issues. One of her top priorities would be health care reform. Sanborn serves on the Legislature’s Insurance and Financial Service Committee and is currently co-chairing a task force looking to reform health care in Maine. As a member of the Legislature’s Energy, Utilities and Technology Committee, she’s interested in things like micro-grids, battery storage, offshore wind and solar technology.