Jamie Gauthier, a political newcomer who built a grassroots campaign, upset longtime Councilwoman Jannie Blackwell on Tuesday, ending a 45-year reign of representation by Blackwell’s family in West Philadelphia.

With more than 96.6 percent of the votes counted, Gauthier held a more than 2,800-vote lead in the Democratic primary, according to unofficial returns.

“I feel so excited and thrilled, this is a victory for the people of the 3rd District,” she said. "They overwhelmingly voted for change.”

Blackwell didn’t concede or give a speech to supporters at a results-watch party. Instead, she walked out around 11 p.m. hugging and shaking hands with supporters and saying, “See ya. Thanks, everybody.” A reporter asked her whether she had anything to say, and she said: “No, I’m going home.”

The former head of the Fairmount Park Conservancy, Gauthier campaigned on the need for change in the district and a better balance of development and gentrification in the changing neighborhoods surrounding University City.

Gauthier also out-fundraised Blackwell early in the race and benefited from the backing of Philadelphia 3.0, a political action committee that spent hundreds of thousands mailing fliers around the district on her behalf. The endorsement was somewhat controversial, because Philadelphia 3.0, which has a nonprofit, did not legally have to disclose all of its donors.

Blackwell was a West Philadelphia institution who took over the seat from her husband, Lucien Blackwell, when he went to Congress. She had not faced many credible challengers since her election in 1992.

The 3rd District has also changed in that span, seeing a six-percent growth in population over the last decade and brisk development in neighborhoods west and southwest of University City.

Gauthier, an urban planner with a master’s degree from Penn, hoped to capitalize on that shift in the district,

On Tuesday, Pam Kane, 56, a midwife who had not been inspired to volunteer for a candidate since President Obama, handed out literature for Gauthier, who she also voted for.

“For me, it’s the commitment to open, honest government,” she said. “The whole councilmanic prerogative thing has got to change. I don’t see how you can have a city that as a whole has rational development, if each ward has control over its own little fiefdom. … Not to mention the corruption.”

Just then, Gauthier herself walked up to shake hands and cast her own vote. She said, voters were energized by opportunity to make a choice, for the first time in a long time.

“We have talked to voters all over the district. No matter what neighborhood I’ve been in I’ve heard the same thing: People are ready for a change. Today, I hope those people who said they want change come out.”

Gauthier said she understood voters’ concerns about the money powering her race, but that it was necessary within the current campaign finance structure and won’t compromise her independence.

“It’s difficult to take on a longtime, entrenched incumbent, and I’ve built a large base of support to help me do that,” Gauthier said. “I’ve been building support among people who are willing to support my agenda. I was clear with the public about my agenda.”

Gauthier’s nomination all but ensures her election in November. No Republican candidate ran in the district.

Staff writer Samantha Melamed contributed to this article.