In most electoral situations, you can’t win unless you’re No. 1. But with San Francisco’s top-three ranked-choice voting system, the mayoral race might come down to who can net the most votes for Nos. 2 and 3.

If he can’t be first, former Supervisor Bevan Dufty is actively seeking to be “in the mix.” With Mayor Ed Lee leading the pack according to recent polls, many of the 11 candidates have adopted an “anybody but Lee” strategy by ganging up on the interim municipal chief who had promised not to seek permanent office when he was appointed in January.

Dufty, on the other hand, has gone out of his way to welcome Lee to the race, even joking that he’d like to serve as his “No. 2.”

Politicos say the overt in-the-mix call is a rarity, but it’s not as dumb as it sounds. Under ranked-choice voting, if no single candidate can achieve a majority, the lowest vote-getter drops off after the first round of counting. The second-place votes from those dropped ballots are applied to their corresponding candidates and treated just like first-place votes during a second round of voting. The process is repeated until a candidate obtains a majority.

“In order to win, you need to have two things going for you if you can’t expect to win a majority outright: a strong core of support with first-place votes and a broad base of support to get the second and thirds,” said Steven Hill, an architect of ranked-choice voting in San Francisco. “You have to have both of those; you can’t just have one.”

If Dufty can maintain his positive message while other candidates try to take shots at Lee, he can position himself away from controversy and presumably into favor with more voters. Dufty laughed at the notion that he is the only candidate with a ranked-choice strategy.

“You mean I’m the only one being honest about my ranked-choice strategy?” Dufty said, mentioning the recent Democratic County Central Committee endorsements of both Supervisor John Avalos and City Attorney Dennis Herrera. “Clearly there was an alliance.”

Critics of Dufty say he’s not seeking the mayor’s seat at all, just a job in a possible Lee administration.

“I have a vision to be mayor, and I’m not threatened by Mayor Lee’s candidacy,” Dufty said. “And I’m not looking for a job.”

The top-three strategy worked for supervisors Malia Cohen and Mark Farrell last year. Neither received the most first-choice votes, but ultimately won once second and third choices were factored in. Cohen’s race went into 20 rounds of counting.

dschreiber@sfexaminer.com