The weekend started with Mark Leno leading the race for mayor, but after tens of thousands of ballots were processed Saturday and Sunday, London Breed pulled ahead.
YOUR VOICE, YOUR VOTE: Bay Area June 2018 Election Day results
Through rank choice voting, both Leno and Breed have more than 100,000 votes, but Breed is now ahead of Leno by more than 1,500.
"We haven't seen the votes this close since I've been here," said Director of SF's Department of Elections, John Arntz. He's been director for 16 years.
VIDEO: Here's how ranked-choice voting works
Arntz says they'll spend the rest of the week counting the remaining 26,000 ballots.
"We're not stressed out, we're not sweating," he said. "This is our process, every election, this is what we do and we seek to have every vote count no matter what the contest is, no matter who the candidates are."
During elections, the Department of Elections turns the ground floor of City Hall into a vote-counting factory. Right now, they are counting provisional ballots.
The workers are here from 8 a.m. to 8 p.m. every single day. On Sunday evening, they're counting ballots that were kicked out of the machine. That might happen, for example, if there's a write-in candidate. And then behind the glass, workers are tabulating actual results.
"It's been a roller coaster of emotions. Every time we come down here, we don't know what to expect," said Tara Moriarty, spokesperson for London Breed's campaign. "She's just waiting and watching like the rest of us. She's very excited to see the outcome because I think for a lot of us here in San Francisco, we feel like we're in a state of limbo."
In a statement, Mark Leno said, "It remains to be seen over the next few days, but it's not over yet."
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.