Six long-shot candidates in the San Francisco mayor’s race qualified for the November ballot by Tuesday’s deadline and will challenge London Breed, all but assuring she’ll easily win her bid for a full term in office.

All of Breed’s challengers come from outside traditional political circles and will be hard pressed to overcome the advantages of incumbency: broad name recognition, campaign experience and fundraising abilities.

Breed beat former state Sen. Mark Leno last June by a scant 1.1% in a special election prompted by the death of then-Mayor Ed Lee. That race decided only who would finish out the rest of Lee’s term, through January 2020. The winner in November will enjoy a full, four-year term before having to seek re-election.

“The only way to beat an incumbent in San Francisco is to prove that they’re either incredibly incompetent or corrupt,” said Jim Ross, a political consultant who managed Gavin Newsom’s 2003 mayoral campaign. “While people aren’t happy with the direction of the city, I don’t think you can prove to voters that Mayor Breed is either of those.”

San Franciscans gave their city government a “B-” grade, according to a biennial survey released last month by the Controller’s Office. Most respondents felt officials had failed to make meaningful progress on its biggest problem — homelessness.

Though it appears Breed will cruise to victory in November, Ross said the mayor’s margin of victory will still be an important barometer of her ability to govern.

“If she can’t get into the high 50s to low 60s, people will really question her strength as a leader, as someone who can drive an agenda in San Francisco.” Rather than rely on her compelling personal narrative, which she used to great effect during last year’s special election, “she’s going to have to tell voters, ‘This is what I’ve done so far and this is what I’m going to do,’” Ross said.

Breed’s six challengers are:

• Ellen Lee Zhou, a public health worker, ran for mayor last June and picked up less than 4% of first-place votes in the city’s ranked-choice voting system. Zhou’s rhetoric and sometimes vaguely outlined policy positions skew conservative. She was one of the featured speakers at a rally convened by right-wing demonstrators last month to denounce perceived censorship of politically conservative views and speech by social media companies. Zhou did not return multiple calls seeking comment.

• Joel Ventresca, a retired administrative analyst with the San Francisco International Airport, plans to attack Breed from the left, touting his bona fides as a neighborhood activist and environmental commissioner. He also ran unsuccessfully for mayor, treasurer and citywide supervisor in the 1990s.

“I’m going to align myself with the mass movements that have made the progressive movement very strong in San Francisco,” Ventresca said. Breed “has associated herself with corporate interests — high tech and the real estate industry.”

• Paul Ybarra Robertson will be listed as a mayoral candidate on the November ballot but listed no contact information or other personally identifying details, according to paperwork filed with the city’s elections department.

• Jean-David Hsu filed to run as an independent Tuesday with a “full focus” on cleaning up the Tenderloin. Hsu submitted his paperwork on time — but just barely. The Department of Elections will review and verify his eligibility for the ballot Wednesday.

• Wilma Pang is a professional singer and music educator who ran unsuccessfully for various offices in the past, including multiple runs for mayor and the District Three supervisorial seat. Her central issue as a candidate, she said, is enhancing cultural tourism in San Francisco.

“We need to do something about boosting our cash cow — that’s the tourist industry,” she said.

• Robert Jordan, a street minister, rounds out the list of longshot mayoral candidates. He filed just before the 5 p.m. deadline and said he was “a hard worker with no ego. I think this is my year.”

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa