Updated Sept. 13, 6:45 p.m.

Facing pressure from New York City Democrats and even his own campaign associates, Bill Thompson is so far resisting calls to concede the Democratic mayoral primary race to frontrunner Bill de Blasio. The public advocate saw a remarkable surge in support in the weeks leading up to Tuesday’s primary, easily ousting the previous Democratic frontrunner Christine Quinn. Current polls show de Blasio at just above the 40 percent vote minimum to secure the nomination, and Thompson has about 26 percent of the vote. The number of uncounted ballots has been reported as anywhere between 16,000 and 60,000.

Thompson must withdraw before midnight Friday -- days before the New York City Board of Elections will begin to count the absentee, affidavit and emergency ballots -- to definitively bypass a runoff election. If Thompson does not withdraw from the race, the decision to force a runoff election will sit solely with the Board of Election’s count of the remaining ballots, a tally that will begin Monday morning. [Update: A recanvassing of ballots submitted at voting precints on Tuesday began on Friday.] If at that point de Blasio’s percentage of the Democratic primary votes is less than 40 percent, the public advocate and the former comptroller will face off on Oct. 1.

On Thursday, the Campaign Finance Board said in a statement that it would would not release funds to the candidates to prepare for a runoff election. “Based on the unofficial results, a runoff election does not appear to be reasonably anticipated,” CFB spokesperson Matthew Sollars said. Later Thursday, Thompson’s campaign fired back at the CFB in a letter, obtained by the New York Daily News, demanding that the funds be released. Pointing out that de Blasio’s hold exceeds the 40 percent threshold by a margin that represents less than a thousand votes, Thompson’s counsel argued that “an 842 vote lead is hardly enough of a margin to declare that it is unreasonable to believe that a run-off primary election will occur.”

One argument against a runoff election is the cost to taxpayers. On Wednesday, a figure estimating the cost of a runoff election at $20 million was bandied about on Twitter, and on Thursday, WPIX 11 ran a story with the headline: “A defiant Bill Thompson says he will push a runoff, even at the expense of taxpayers and fellow democrats.” In fact, a runoff election comes with a still-handy price tag of $13 million, according a Board of Elections spokesperson, who explained that the cost of a general election is roughly $20 million -- likely where Wednesday’s number came from. In any event, a runoff election is almost certainly happening, whether or not Thompson concedes or if de Blasio’s percentage drops below the minimum after all votes are counted -- for the New York City public advocate office. The frontrunner in that race, Letitia James, has fallen short of the 40 percent threshold by a few percentage points, with Daniel L. Squadron not far behind. The BOE spokesperson confirmed that adding a second race to the public advocate runoff would not add anything to the cost of the election.

An argument in favor of a runoff for the Democratic mayoral nomination is the assurance that all votes are counted, something Thompson has insisted on. “It’s an obligation to the voters, to the process, to make sure every vote is heard and every vote is counted, every voice gets heard in this and that someone does get to 40 percent,” he told reporters Wednesday after a 9/11 memorial ceremony.

While it is certainly an empirical possibility that Thompson could end up crossing the 40 percent threshold after the remaining votes are counted, in order to overtake de Blasio, he will need a percentage that is disproportionate to the voting patterns demonstrated thus far. Democratic operative Michael Freedman-Schnapp is among those skeptical of Thompson’s chances, given de Blasio’s success. “[de Blasio] won both Brownstone Brooklyn and central Brooklyn, which is very rare,” Freedman-Schnapp said.

A runoff would delay de Blasio’s ability to shift into general election mode, as he will need to focus on his immediate opponent instead of Joe Lhota, the Republican mayoral nominee. Likewise, Lhota will not right away have a clear opponent to target in his campaign if the Democratic nominee is not determined until next month. In either case, Lhota, a moderate Republican who supports marriage equality and marijuana legalization, will likely to continue to actively court Democratic voters.

Aware that Democrats outnumber Republicans 6:1 in New York City, Lhota acknowledged in an appearance on WNYC’s "The Brian Lehrer Show" Thursday that he needs “as many crossover votes as possible” to win the general election on Nov. 5. And for now, he seems confident he can get them.

“The number of Democrats coming to me, voluntarily coming to me, talking about wanting to vote for me, is extraordinary,” Lhota said. “It’s been happening since late last week, even before the primary results came in. I’m very excited about that.”

New York City has not elected a Democratic mayor since voting David Dinkins into office in 1989.