(CNN) Democratic Rep. Mike Capuano has conceded defeat to Boston city councilor Ayanna Pressley in the Massachusetts primary for his US House seat Tuesday, the latest upset to rock the Democratic Party and showcase a restive base eager for change.

Pressley's win comes less than three months after Alexandria Ocasio-Cortez ousted the No. 4-ranking House Democrat, Rep. Joe Crowley of New York, in a primary.

In his concession speech, Capuano said the district was clearly upset with the status quo and that he shared those feelings.

"I will tell you, I'm sorry it didn't work out but this is life and this is OK. America is going to be OK," Capuano said, adding, "Ayanna Pressley is going to be a good congresswoman and Massachusetts will be well served."

Unlike Ocasio-Cortez, Pressley did not argue that Capuano was too moderate. In fact, she said, the two would vote the same way. Instead, the 44-year-old Pressley -- already a rising star in Democratic politics -- cast the race as about Democrats' need for a new, more assertive style in the Donald Trump era.

Read More