Susan Gorin widened her slim advantage over rival John Sawyer in what had been a neck-and-neck race Tuesday night for an open seat on the Sonoma County Board of Supervisors.

With a majority of mail-in ballots counted in the county's 1st District and all 104 precincts reporting, Gorin led Sawyer by 51.5 percent to 48.2 percent.

Out of 39,215 votes reported by 1:30 a.m. today, the longtime rivals on the Santa Rosa City Council were separated by 1,299 votes.

The margin had not changed by mid-morning and is not expected to until county election officials finish counting votes on an thousands of mail-in and provisional ballots turned in Tuesday. That process could take weeks, officials said.

In results released after midnight, Gorin's lead grew from a slimmer margin of around 400 votes, the difference between the two candidates most of Tuesday night. Gorin and Sawyer are vying to replace retiring Supervisor Valerie Brown.

Early Tuesday night, Gorin, 60, said she was not "taking anything for granted," but said it was "gratifying that a grass-roots organization seems to be prevailing in the race."

If Gorin's lead holds, and some political observers said there is a good chance it could, the six-year Santa Rosa councilwoman and former mayor would take over in January from Brown, a veteran in state and local government who has represented the 1st District since 2002. It includes Sonoma, Sonoma Valley and parts of eastern Santa Rosa.

Gorin's election would mark a triumph for the county's more liberal political interests that have been unable for decades to secure a solid majority on the Board of Supervisors.

A victory by Gorin likely would shift the board to the left on a range of issues, with at least three of the five members, including Supervisors Shirlee Zane and Mike McGuire, favoring tighter oversight of land use, often the most controversial matter for the board. It also could herald a different approach to decisions on county services, including roads, parks and open space and aid programs.

The shift would take the majority away from the centrist block of politicians that long have decided the board's stance on most high-profile issues. That block currently includes Brown and Supervisors Efren Carrillo and David Rabbitt.

A surge of votes for Sawyer would maintain the current majority.

Of 185,000 mail-in ballots sent out across the county, 65,000 hadn't been returned as of Monday night. County election officials expected 35,000 would be turned in Tuesday, and about 7,000 might come from the 1st District, said Janice Atkinson, the county's elections chief.

Still, Atkinson confirmed the number of mail-in ballots that arrived in time to be counted on Tuesday represented a majority of the 1st District's mail-in votes. She said her office would have a tally of the uncounted mail-in ballots in the district by the end of the week.

Before midnight Tuesday, Sawyer said he was still optimistic about his prospects for victory. "I just have this feeling that the voters in Sonoma Valley understand my commitment to them and are going to vote my way," he said.

The high-stakes contest was bitter at times, featuring blistering attacks from both sides.

Sawyer was better-funded throughout, with backing from building and real estate interests, as well as labor groups representing law enforcement.

As the proprietor of his family's now-defunct downtown news store, he was first elected to the Santa Rosa council in 2004. His second City Council term will end next month.

Gorin, a former community volunteer, Santa Rosa schools trustee and planning commissioner, would forgo the second half of her second council term to assume the county job.

The election marks a change for the 1st District regardless of who wins. Both candidates live within Santa Rosa city limits, meaning the district's representative will, for the first time in at least two decades, live outside Sonoma Valley.

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.