“Bring it on,” a surprised Ms. Davis told Politicker during an interview Sunday night, moments after learning that Mr. Spitzer was planning to jump into the electoral arena days before the petitioning deadline. The news also shocked the city’s political establishment and turned the formerly uncontested race on its head.

“Gosh, it’s going to be a fun race!” she exclaimed.

Ms. Davis, of course, isn’t new to politics. She ran against Andrew Cuomo in the 2010 governor’s race, and has been long been mulling a run for citywide office on the independently-petitioned Libertarian Party line, first throwing her hat into the mayor’s race and then looking elsewhere for a potential long-shot bid. (Mr. Spitzer is challenging front-running comptroller candidate Scott Stringer, Manhattan’s borough president, in the Democratic primary.)