With less than two months to go before the election, 20.6% of voters said they’d vote for Farrell as their first choice while 20.3% said they’d back Breed in the KRON4 News/Emerson College Poll. Daniel Lurie, a nonprofit executive and heir to the Levi’s fortune, is not far behind with 17.5% of voters backing him as their first choice.

Twenty-seven percent of voters surveyed remain undecided on the crowded and competitive field. There are 13 candidates in the running.

“It is the undecided vote that is ahead in this poll,” Sonoma State University political science professor David McCuan told KRON4. “But as voters begin to turn their attention, some interesting things happen as we start to look at second and third choices.

“People like Mayor London Breed begin to fall, and other candidates replace and move up to a higher place. That is, who is the second and third choice becomes important. And that’s when someone like Daniel Lurie rises, London Breed falls, Mark Farrell falls, and undecideds stay about the same. As we move to third choice, then things get really interesting because London Breed kind of holds her own and Daniel Lurie falls.”

This is the first time in several years that San Francisco will have a mayoral election in the same cycle as a national general election, which will likely prompt a higher voter turnout.

San Francisco uses a ranked-choice voting system, which could delay the results for a week or more after the election. Under the system, voters rank candidates from their first choice to their least preferred. In multiple rounds of tallying, the candidate who receives the fewest votes is eliminated and their supporters’ votes are carried over to the voters’ next preferred pick until there is a winner.

The new poll comes as Breed announced she will skip Wednesday night’s mayoral debate. Breed, who had confirmed her attendance in April, told CBS News Bay Area on Tuesday that a timing issue led to her pulling out at the last minute.

“I am the mayor of San Francisco, not just a candidate,” she said. “I have to run the city, and that includes meetings and everything else that I need to do, so I have to be very selective about the number of the debates and the amount of time I’m able to be available for these kinds of opportunities.”

McCuan said voters will notice the vacancy and warned that it could backfire on Breed.

“San Francisco voters are hyperpolitical and hyperengaged, and when [they] see you are not on the stage, that does send messages,” he said. “I expect them to talk a lot about the person not on the stage, and that means that what all of them have in common is the challenge to Mayor Breed. … They can talk about issues that are important to them and their candidacies, but they can also talk about her absence and how that speaks volumes.”

Farrell accused Breed of ducking the debate because “she doesn’t want to defend her track record of failed leadership on the top issues facing our city.”

Laurie also had some harsh words for the mayor.

“After six years as mayor and six as a supervisor, London Breed is dodging the voters instead of speaking to them because she can’t defend her record of growing and exploiting the city’s corrupt bureaucracy,” his campaign said in a statement. “Daniel Lurie is the only candidate with the right experience to change the broken system at City Hall and voters deserve to hear why. Ultimately, change is coming to San Francisco whether or not the mayor is afraid to stand on the stage with Daniel.”