Elections officials are expected to release additional results Wednesday afternoon. As of Tuesday night, voters were narrowly approving the state's new "everything but marriage" law that marks a significant expansion of rights for gay couples.
With about 50 percent of the expected vote counted, Referendum 71 was leading 51 percent to 49 percent.
The measure asked voters to approve or reject the final expansion to the state's domestic partnership law, which grants registered domestic partners additional state-granted rights currently given only to married couples.
Meanwhile, in Seattle, environmentalist attorney Mike McGinn is holding to a slim lead over T-Mobile executive Joe Mallahan in the race to be the city's next mayor.
McGinn went ahead of Mallahan after election day's initial count. With 38 percent of the expected vote counted Tuesday night, about 84,000 votes, McGinn led Mallahan by just 910 votes.
King County officials will release more votes Wednesday afternoon.
On Tuesday night, McGinn was cautious about his lead, saying that elections take a long time to be decided in Washington. Mallahan said he was optimistic the remaining votes will lean his way.
In the August primary, McGinn and Mallahan outpolled Mayor Greg Nickels, a two-term incumbent, after he was dogged by criticism of the city's response to a December snowstorm that paralyzed Seattle for nearly two weeks.
CBSNews.com Election Night Coverage:
What McDonnell's Win Means for the GOP, Obama
Corzine's Fall Has Been Festering for a While
What Doug Hoffman's Loss Means to Conservatives
Lessons for the White House from '09 Election Results
Why Christie Won in New Jersey
McDonnell Won Due to Turnout, Independents
Exit Polls in Va. and N.J.: The Obama (Non) Factor?