Massachusetts Sen. Ed Markey has fended off the highest-profile Democratic primary challenge of his decades in federal office, defeating the rising Rep. Joe Kennedy III, a member of the state's legendary political dynasty.

Kennedy conceded the contest nearly two and a half hours after polls closed Tuesday night. The Associated Press projected Markey as the winner a short time later.

Prior to this race, no member of the Kennedy family had lost an election in Massachusetts, according to the Cook Political Report.

Markey's victory means the 74-year-old incumbent, who became a Massachusetts congressman before the 39-year-old Kennedy was born, advances to November's general election and will likely continue to represent the solidly liberal state in the Senate for another six years, while Kennedy — at least for a time — will be out of Congress, since state law prohibited him from running for reelection to his House seat and in the Senate primary at the same time.

The outcome adds a new twist to an emerging narrative in Democratic politics. Over the last two years, young progressive challengers have toppled well-known longtime incumbents in places like St. Louis and New York City.

In the Massachusetts race, though, it was Markey who received support from progressive figures and organizations for his reelection, and his challenger, Kennedy, whose famous surname boosted his name recognition.

Indeed, before Kennedy even entered the race, polling found him to be the favorite — and some analysts were counting Markey out.

But Markey ran up big margins in Boston and many of its well-heeled surrounding communities, eclipsing Kennedy's advantages in more working-class cities.