Democrats Evan Low and Joe Simitian each garnered 16.6% of the vote with 30,249 votes each, according to unofficial state results on the California Secretary of State’s website for the 16th Congressional District.
They’ll both have their names on the ballot, along with fellow Democrat and first place finisher Sam Liccardo, unless a voter requests a recount.
NBC News has projected that Liccardo, with 21.1% of the vote, will advance to the general election.
San Mateo and Santa Clara counties both released their official results on Thursday, starting the clock for a five-day period when voters can call for a recount.
The candidates are vying to fill the seat being vacated by Democratic Rep. Anna Eshoo, who announced in November that she would not seek re-election after serving in Congress since 1993.
In California primaries, the two candidates who receive the most votes move on to the general election, regardless of their political party. But a tie in the top two spots means those candidates advance.
“It’s the kind of thing that is very low probability of ever happening, but they foresaw it in the law and created this rule that they go into the runoff together,” said Paul Mitchell, the vice president of voter data vendor Political Data Inc.
Any voter can request a recount, but in doing so they have to front the associated costs. Mitchell estimated that a recount could cost as much as $325,000.
Low or Simitian could also request a recount.
“I think that you’re only going to want to request a recount if you’re pretty sure you’re going to win it,” said Justin Levitt, a law professor at Loyola Marymount University in Los Angeles.
“You need an awful lot of confidence to make sure that you win by one rather than losing by one at this point,” he added.
Low is a California assembly member, and Simitian is a Santa Clara county supervisor.
“This historically close race shows that every vote really counts,” Low said in a statement. “I could not have made it this far without every one of you, and I hope to earn your support once again in November.”
In his statement, Simitian said “this is what a functioning democracy looks like.”
“Sometimes it takes a while for democracy to work,” he said. “This has been one of those times. Call it a cliffhanger, a rollercoaster, a wild ride — but it has absolutely been worth the wait!”
Neither campaign directly responded to questions about whether they would request a recount.
Liccardo could also call for a recount if he wants to try to avoid being in a three-way race.
But, Mitchell said, “it’d be kind of weird” for him to do that.
Liccardo, the former mayor of San José, did not immediately respond to a request for comment Thursday night.
This article was originally published on NBCNews.com