CHANGE HAMMERED ON US Rep. Michael Capuano’s door at about 9:15 Tuesday night after making the rounds at a few other stops. It couldn’t wait.

For Ayanna Pressley, the 44-year-old Boston City Councilor who defeated the 10-term incumbent by a surprisingly wide 59 to 41 margin, the result justified the politically risky decision she made nearly seven months ago to challenge an entrenched Democrat whose progressive voting record would not be much different than hers if she won.

“It seems like change is on the way,” Pressley told her giddy backers at the IBEW hall in Dorchester, punctuating her sentences and urging her supporters to join in with “change can’t wait,” her signature slogan. “I knew we would find no favor with the Democratic establishment. I knew I would be demonized as entitled and what no woman can ever be – ambitious.”

Pressley’s victory is the latest earthquake to shake the ground beneath the Democratic establishment. Her win follows that of Alexandria Ocasio-Cortez in New York who defeated another 20-year incumbent in US Rep. Joe Crowley, an upset that made Capuano take notice.

Pressley, the first black woman in the Boston City Council, will be the first person of color from Massachusetts elected to the House of Representatives, since there is no Republican nominee. In her victory speech, a clearly stunned Pressley praised Capuano’s service but took on the Democratic gatekeepers, mostly white men, as much as – probably even more than – she slammed President Trump.

“While our president is a racist, misogynistic, truly empathy-bankrupt man, the conditions that made the [7th Congressional District] one of most unequal in America was cemented in policy long before he descended on the escalator in Trump Tower,” she said. “Some of those policies were put in place with Democrats in the White House and in control of Congress.”

In a brief concession speech just 75 minutes after polls closed, Capuano took to the stage at his somber election party in his hometown of Somerville and put his defeat in context with the loss of state Reps. Jeffrey Sanchez and Byron Rushing, whose districts are part of the 7th Congressional District.

US Rep. Michael Capuano.

“Clearly the district wanted a lot of changes,” Capuano said in his 90-second speech. “Apparently, the district is very upset with lots of things that are going on. I don’t blame them. I’m just as upset as they are. But so be it, this is the way life goes.”

Pressley was outspent and Capuano had the benefit of most of the establishment endorsements regardless of race, including US Rep. and civil rights icon John Lewis, former governor Deval Patrick, and Boston Mayor Marty Walsh. Polling consistently showed Capuano with a lead, albeit not an insurmountable one, with a sizable number of undecideds.

Katjana Ballantyne, president of the Somerville Board of Aldermen and one of three board members to endorse Pressley, said young people of color in the violence prevention program she ran in Dorchester got excited when they met Pressley in 2012. That same excitement reverberated in the congressional race.

The teen mentors we had, “they were just buzzing,” said Ballantyne. “There was a woman who looked like them that was just listening to them. Told them they were worthy. And that means something. People just want to be heard.”

Erin O’Brien, political science professor at the University of Massachusetts Boston, was one of the few pundits who predicted an outright Pressley win but said she expected a tight race to go into the wee hours of the morning. When Somerville showed Capuano with a slim 0.7 percent victory in the city he once served as mayor, it was clear change was in the air.

“It’s anecdotal,” O’Brien said of her sense that Pressley had the momentum, “but you could feel the passion behind her supporters. The energy was on her side. There was no way to poll this race because you didn’t know who was going to show up… She’s shown she can get her folks to the polls.”

Indeed, Pressley was the top vote-getter in council elections the last three cycles and the whipping she gave Capuano in Boston neighborhoods proved her mettle in bringing voters out to the polls. O’Brien said with the differences in ideology being so slim, turnout by the challenger needed to match her message of change in representing the state’s only majority-minority district.

“If you’re a Democrat, he’s a good progressive, but voters were looking for someone who looks more like the district,” said O’Brien. “In a perfect world, you’d have both those individuals in office. What’s changed is who turned out. She was the right person at the right time. I don’t know many Democrats who hate Capuano and love her…It’s very rare to have a challenger from inside your party unless there’s a scandal or a huge ideological difference.”

Michelle Wu, Pressley’s colleague on the City Council, said Pressley brings what people want to her new job – a voice and an advocate.

“This is so much emotion wrapped up in a room of people who are both breathless and astonished but also affirmed,” said Wu. “I think everybody here felt like the entire campaign, momentum was building, and the response out in the community was clear – that people wanted a new type of bold, activist leadership.”

Attorney General Maura Healey, arguably the state’s most popular Democrat, endorsed Pressley in returning the favor when the one-time congressional aide supported her insurgent campaign in 2014. Healey said the polls and the pundits never dissuaded her from believing Pressley would pull it out.

“I’m not surprised, and I’m delighted,” Healey said amid the celebration at the electrical workers’ hall. “Ayanna will be a terrific congresswoman. I believe so much in her smarts, her passion, her fearlessness, and her compassion for people. We need that in Washington. It didn’t really matter what the pundits or the pollsters said. I knew Ayanna and I know what she’s about, and I knew what she would deliver.”