The Bay Area’s only GOP lawmaker in either the Legislature or Congress, East Bay Assemblywoman Catharine Baker, became the latest California Republican to lose her seat to a blue wave of Democratic votes.

Baker conceded to Democrat Rebecca Bauer-Kahan on Friday afternoon, just hours after she lost the lead she had held since election day.

“I have just called my opponent, Rebecca Bauer-Kahan, to congratulate her on winning election to the State Assembly for District 16, and to wish her success,” Baker said in an email to supporters. “While there remain many ballots to count, the outcome is not expected to change.”

Baker’s race is following a pattern seen throughout California — as thousands of votes have been counted since election day, Republican candidates’ leads have shrunk and, in many cases, disappeared altogether.

Baker, a two-term incumbent from San Ramon, had an election night lead of 51.2 percent to 48.8 percent over Bauer-Kahan, a law professor from Orinda. The gap was down to fewer than 200 votes before Friday, when a fresh infusion boosted the Democrat into a lead of 2,170 votes — 102,500 to 100,330, or 50.5 percent to 49.5 percent.

Baker is an anomaly in the Bay Area, where Democrats are firmly in control. That includes her 16th District, where the party holds a 41 to 27 percent voter registration advantage over Republicans.

Baker distanced herself from national Republican orthodoxy during the campaign, touting what she called pro-choice, pro-environment and pro-gun control positions to voters in a district that stretches from Lafayette and Walnut Creek down through Livermore.

Bauer-Kahan, a first-time candidate, questioned whether Baker is all that different from other Republicans. She noted that although the incumbent played up her pro-choice stance, it was Bauer-Kahan who won the endorsement of Planned Parenthood.

In other races, Democratic state Sen. Ricardo Lara of Bell Gardens (Los Angeles County) was declared the winner in the contest for state insurance commissioner. While independent Steve Poizner held the lead on election day, Lara pulled ahead and now leads by nearly 300,000 votes, 51.6 to 48.4 percent.

Lara will be the first openly gay person to be elected to statewide office in California.

An estimated 2.5 million votes remain to be counted in the state.

In Orange County, Democrat Gil Cisneros of Yorba Linda now leads GOP businesswoman Young Kim of Fullerton by nearly 2,300 votes. Kim, a former assemblywoman, held the lead until Thursday evening.

In the Central Valley’s 21st District, Democrat T.J. Cox crept closer to GOP Rep. David Valadao of Hanford (Kings County). Valadao’s lead is now about 1,750 votes, 50.9 to 49.1 percent.

Those races are two of the last congressional races yet to be called in the country. On Friday morning, Orange County GOP Rep. Mimi Walters conceded to Democrat Katie Porter, acknowledging the UC Irvine law professor’s growing lead.

Trapper Byrne and John Wildermuth are San Francisco Chronicle staff writers. Email: tbyrne@sfchronicle.com and jwildermuth@sfchronicle.com. Twitter: @trapperbyrne @jfwildermuth