Chan received a whopping 54.6 percent of the vote in a four-candidate race in District 3, which includes San Leandro, Alameda, San Lorenzo, Ashland, Hillcrest Knolls and parts of Oakland, so she won't have to face a runoff in November.
Alameda Mayor Bev Johnson finished second with 30.7 percent, financial planner Harold Lowe was third with 7.6 percent and retired businessman and perennial candidate Lou Filipovich was fourth with 6.6 percent.
Chan, who served in the state Assembly and eventually became majority leader after she left the Board of Supervisors, said her priorities are solving the county's budget problems while protecting health and senior programs, improving access to quality education and creating jobs.
She will succeed Alice Lai-Bitker, who is stepping down at the end of the year after 10 years in office.
In District 2, which includes Hayward, Newark, Union City and parts of Fremont and Sunol, no one got 50 percent of the vote.
Alameda County Family Justice Center executive director Nadia Lockyer finished first with 38 percent of the vote but she will face a runoff in November.
It appears that she will face former state Senator and Assemblywoman Liz Figueroa, who was second with 24.94 percent of the vote.
But Union City Mayor Mark Green finished a close third with 23.78 percent of the vote and only trails her by 263 votes, so there's at least an outside chance that a tally of uncounted absentee ballots could alter the race.
Hayward Councilman Kevin Dowling finished fourth with 12.9 percent.
The winner of the November runoff will succeed Gail Steele, who is retiring after 18 years in office.
Lockyer, the wife of state Treasurer Bill Lockyer, said in her ballot statement that she wants to promote economic growth, make government more efficient and create healthy families and safe communities.
Figueroa said she wants to recruit green and biotech companies, sustain public safety resources, and preserve and enhance health care options so families don't have to choose between paying their mortgage or health care costs.
Green, who has been mayor for 16 years, said he has the experience to make the hard choices necessary for the county to address its difficult budgetary issues.
Hayward planning commissioner and retired budget Marvin Peixoto won a spot on the City Council by finishing first in a six-person race for two open seats with 29.8 percent of the vote.
The seats are being vacated by Dowling and Anna May.
College instructor Mark Salinas won the other open seat by finishing second with 25.3 percent of the vote.
Sara Lamnin, the program director for the Hayward Community Action Network and chair of the Hayward Citizens' Advisory Commission, finished third with 19.8 percent.
Food and beverage broker Ralph Farias, Jr. was fourth with 9.8 percent, retired business owner Steve Oiwa finished fifth with 7.5 percent and security guard Lawrence Fitzpatrick was sixth with 7.2 percent.
Peixoto said his priorities are fighting crime, economic development and improving the city's image.
Salinas said he wants to ensure full funding for the city's police and fire departments, focus on economic development and job creation and spend money to clean up neighborhoods and parks.
Michael Sweeney, who was running unopposed, was easily re-elected mayor of Hayward with 97.4 percent of the vote. The other 2.6 percent went to write-in candidates.
Sweeney said his priorities are fighting crime and boosting public safety, cleaning up the city, making it "greener" and improving its public schools.
Administrative law judge Victoria Kolakowski led a three-way race for an opening on the Alameda County Superior Court bench with 45 percent of the total vote.
She will face Deputy District Attorney John Creighton in a runoff election in November, as he finished second with 32 percent of the vote.
Attorney Louis Goodman finished third with 22 percent.