Mike McGinn addresses supporters on Tuesday night.

According to the first numbers released by King County, McGinn has 50.03 percent of the vote, and Mallahan has 48.96 percent.

About 85,000 ballots have been counted in the race so far, and King County's next update is not until 4:30 p.m. on Wednesday.

Less than 1,000 votes separated the two candidates

On Tuesday night McGinns' campaign left automated voice messages on supporters' phones, urging anyone who hasn't yet voted to bring their ballots to the QFC store in Lake City.

The message said ballots will be accepted until 11 p.m., then brought to "the airport post office." The Riverton Heights Post Office at 15250 32nd Avenue South in Tukwila is open until midnight on weekdays.

Mallahan and McGinn are two political newcomers. Both outpolled Mayor Greg Nickels in the August primary and advanced to Tuesday's election. Nickels had been dogged by criticism of his handling of a snow storm last year.

Following the primary, Mallahan and McGinn - both Democrats - set out to establish their names among Seattle voters. The position is technically nonpartisan.

Mallahan won key endorsements from established local politicians - including Gov. Chris Gregoire; business organizations, and labor unions, largely because of his support for a highway tunnel under downtown Seattle that would replace the earthquake-damaged Alaskan Way Viaduct.

McGinn made opposition to the tunnel a centerpiece of his primary campaign, but softened his position a few weeks ago. His campaign highlighted experience he had leading parks levy campaign and his activism with the Sierra Club, the national environmental organization.

"We're very gratified that we have a lead on election night. It was a very close race," McGinn said.

But the winner of this race will likely not be known for days.

At a popular park in Seattle on Tuesday, voters queried about the election were split on their choice for mayor.

"I ended up voting for Mallahan because I felt that the whole thing about the tunnel was a mess. I thought let bygones be bygones and just move on. I didn't want to have any more studies," 41-year-old Seattle resident Anne Aliverti said.

Meanwhile, Krista Means, a 41-year-old stay-at-home mom, said she voted for McGinn, but that if Mallahan wins, she wouldn't be disappointed.

"I just like the way McGinn was looking down the road for ways of getting around the city, using your bike, using mass transit ... I liked his vision," she said.