(Updated on Thurs., Nov. 5, 4:15 p.m.)— Andrea Campbell, a 33-year-old Mattapan resident who emerged from political obscurity this year to mount her first-ever run for office, defeated the city’s longest serving political figure on Tuesday in decisive fashion, notching a 62-38 point win over 32-year-incumbent Charles Yancey.

“This campaign really set out to mobilize as many people as possible,” a jubilant Campbell told the Reporter as her victory became obvious. “I look forward to fulfilling my promise.”

The new councillor added, “It’s nice to know we got the message out to the people who went out and voted. Our goal was always to have a large amount of volunteers out on doors to get out the vote. They got out and spread our message and that’s what the voters heard.”

Campbell rode a tide of momentum that was unleashed by a startling victory in September that revealed deep fissures in Yancey’s previously rock-solid electoral foundation. Aided by a flurry of endorsements from prominent political figures – from Sheriff Steven Tompkins to Attorney General Maura Healey – and labor organizations, Campbell mounted an impressive ground attack on Tuesday that built on her September surprise.

Yancey’s reaction to the vote at a post-election gathering spoke to his disappointment at the turnout. “We know that a lot of people who should have gone to the polls didn’t go to the polls,” he said, while assuring those gathered in the hall that they should have no regrets, that “a lot did go right in this campaign.”

Campbell’s strongest showing on Tuesday was in the ward where both Campbell and Yancey reside.

The precincts of Ward 17s drew the highest number of District 4 voters throughout a day of low turnout (13.6 percent) across the city.

Yancey managed to win in only six of the district’s 32 precincts, including four precincts in Ward 14, but even in those instances the margins were much tighter. Campbell tacked on lopsided wins in the district’s two Roslindale precincts, eclipsing 80 percent wins in 19-2 and 18-7.

And she overwhelmed Yancey in his own backyard, earning 79 percent of the vote at the Codman Apartments on Washington Street, which consistently posted the highest percentage turnout in the city throughout the day. Yancey won just a single precinct in Ward 17 – the Codman Square Tech Center’s 17-1 – by a margin of 85-76 votes.

Campbell campaign manager Katie Prisco-Buxbaum said their camp was smart, efficient, and coordinated. They identified “high voter turnout briefings where we knew they would show up” based on the preliminary, and mobilized their 200-some volunteers to get out the pre- and post-work voting push. Thousands of calls poured out from two Campbell phone banks, she said. One was geared toward elderly voters who needed rides to polls, the other toward undecided and non-elderly voters.

“We did a full pass of the entire universe of Campbell supporters,” Prisco-Buxbaum said.

Two precincts in particular — Ward 14 Precinct 2, the Sarah Greenwood School, and Ward 18 Precinct 1, Groveland Senior Center off River Street— had seen a close tally in the preliminary and the Campbell team was bracing for a challenge in the general election, Prisco-Buxbaum said. So, she said Wednesday morning, “We were pleasantly surprised to find we had a margin there.”

As Yancey supporters awaited the arrival of their candidate at the Unity Sports & Cultural Club on Dunbar Avenue, one of Yancey’s stalwart allies, Rep. Gloria Fox of Roxbury, called his defeat “a loss for the community. It was unfortunate that all that money came into our community just to unseat an incumbent,” she said.

Speaking before the councillor reached the stage, Fox said the city would come to regret the voters’ choice, but, more importantly, she said, Yancey was not done yet.

“For a man like Charles Yancey, the work begins again,” she said. “From this day forward, he’s still going to be in this community. He’s still got work to do.”

Former state Sen. Dianne Wilkerson, who also spoke to the small crowd before Yancey arrived, was direct in her critique: “I’m not sure what we got, but I damn know for sure what we lost,” she said, calling Yancey the right kind of “old school” who was responsible for everything good in the community.

Once he arrived at the hall, Yancey rarely let his smile dim. He beckoned his family to join him on stage, where they flanked him during a concession speech that made no direct reference to his victorious challenger, who was celebrating her win at the Blarney Stone.

As some in the audience sobbed, Yancey said he left a tangible legacy to be continued, including police body cameras and a civic review board. “I’m not going away. Our work is not done yet,” he added.

Yancey had faced stiff opposition before, most notably a 2003 challenge from Egobiduke Ezedi, a minister whose alliances with Yancey’s white colleagues on the council became a central theme in Yancey’s defense. Buoyed by public sup- port from established African-American leaders like Wilkerson and Councillor Chuck Turner, Yancey surged to a 10-point win over Ezedi in the November final.

But things have changed dramatically since 2003, and not just in the composition of the city’s political leadership. The Fourth district itself was significantly altered in the last round of redistricting, with several Mattapan precincts shifted into District 5, now held by Hyde Park’s Tim McCarthy. Yancey has long been linked to Mattapan, even though he has never lived there (he resides in Dorchester’s Melville- Park neighborhood.)

Still, some of Yancey’s most prominent successes on the council involved Mattapan, where he claimed credit – with some merit – for pushing for amenities like a new Mattapan branch library, a community center at Mildred Avenue, and a modernized Boston Police station house on Blue Hill Ave.

At Tuesday night’s gathering, he said that he was still committed to getting a Mattapan High School built.

Campbell, who seized on her own personal story of perseverance amid very difficult child- hood circumstances in Boston, sold a message of youthful energy and efficiency throughout her campaign, which really began in earnest in December 2014.

A Boston Latin School graduate who went on to attend Princeton University before becoming an attorney, she gained experience working in the administration of former Gov. Deval Patrick. Campbell’s campaign saw an infusion of the sort of donations that often elude first-time candidates, especially those who are targeting longtime incumbents. By the spring, she had outstripped Yancey’s numbers by raising nearly $35,000, with some of the money coming from prominent Democrats seeking to reinforce promising female candidates.

Tuesday night’s celebration at the Blarney Stone was “surreal,” Prisco-Buxbaum said, adding that “for so many people in that room who had given so much, and had called their family and friends and said ‘go out and vote,’ this is a reflection of their hard work.”