RELATED: Bay Area election results
The last time ABC7 News checked, Mark Leno had 50.4 percent and London Breed had 49.6 percent of the vote.
"Nothing is final yet," said John Arntz, the Director of Elections for San Francisco. It's expected to take days, if not weeks, before we know for sure.
Approximately 80,000 ballots remain to be counted, a process which could take several weeks.
While the race appears to be down to two candidates - London Breed and Mark Leno - due to the city's ranked choice voting system, no candidate has been officially eliminated. Each ballot tally is run fresh to properly calculate the ranked choice.
About 4,700 additional votes were counted Wednesday. Approximately 70,000 vote-by-mail ballots need to be processed and may be completed by Monday. To be valid, those ballots must have been postmarked on or before June 5 and received no later than three days after the election. Then, staff will begin to count provisional ballots.
It will take at least to next week to count all ballots, and may take several weeks to complete all counting.
The Director of Elections says he was surprised by the turnout in Tuesday's primary, which he estimates at 50 percent.
"What we experienced yesterday in San Francisco was essentially like a presidential election election day." The California Secretary of State's office has issued a preliminary report on voter turnout and marked San Francisco with 32 percent, the highest of all nine Bay Area counties.
The situation, according to Alex Clemens of Lighthouse Public Affairs, is fluid.
RELATED: Roundup of California primary election results
"It can be resolved earlier if trends show that one of the candidates is separating from the other, but I think both candidates are settling in for late nights, chewing fingernails and lots of lawyers," Clemens said.
What appears to be clear is that the alliances formed between Mark Leno and Jane Kim a month ago seems to be favoring Leno because of the rank choice voting system.
With Kim out of the race, 75 percent of her voters, or 25,000 votes, have gone to Leno as a second-place candidate - with only 7,500 transferring to Breed.
VIDEO: Here's how ranked-choice voting works
"What is encouraging is that it suggests what I had set as my goal, which is to build a very broad case coalition of support from day one," Leno said.
The rank choice voting system has always been controversial. Gavin Newsom, former mayor now running for governor, said it's still confusing to him.
"I've never been an advocate for it. I don't think it's good for this city or this state," he said.
See see how the ranked-choice voting unfolded by each round here.
Get all the latest Election Day 2018 stories and videos from ABC7 here.