Erlene DeMarcus received 6,099 votes, 18.14%, while Mike Harris, who dropped out of the race in September, pulled in 13%, receiving 4,381 votes.
About 35 people turned out at Brown's home Tuesday evening to await results and by 8:30 p.m., she had claimed victory. Brown chalked up the win to local support.
Pleasanton residents were "voting for a candidate that stands for their city," Brown said. "I represent the citizens of Pleasanton."
Among those celebrating at Brown's event were Pleasanton City Councilwoman Cindy McGovern, who is termed out this election, and former Pleasanton Councilwoman Kay Ayala.
Nearly the same number of Pentin's supporters gathered at Girasole Grill on Santa Rita Road.
Pentin, a longtime member and current head of the City Planning Commission credited his win to voters recognizing his leadership and experience.
Erlene Demarcus was among a dozen or so waiting the results of state and local elections at Democratic Headquarters on Stoneridge Drive. She said she entered the race as an act of public service, "but somehow it turned out not to be about the issues."
Demarcus, who has served on BART's board of directors, ran into recent criticism for accepting donations from a developer.
Both Brown and Pentin said they have specific issues they plan to address once they're sworn in to office.
Brown is a member of Pleasanton's Eastside Specific Plan-Task Force, and hopes to bring questions about potential development in the quarry area to City Council. Pentin wants the city to continue its work on Bernal Community Park and a wooded area at the park to be called Oak Woodland.
While Pentin said the current City Council had done much to rein in pensions, he said the new council will be called on to do more of the same.
"It is a major shift in the council and we have some work ahead of us," Pentin said.