In what could be a stunning upset in the race to be Los Angeles County sheriff, challenger Alex Villanueva took a narrow lead over Sheriff Jim McDonnell early Wednesday.

With 100% of precincts reporting, Villanueva, a retired sheriff's lieutenant, was ahead by 4,927 votes, but provisional and late mail ballots still have to be counted, reports the Los Angeles Times.

Heading into the election to run one of the nation's largest law enforcement agencies, McDonnell and Villanueva had been expected to be locked in a tight race.

Sheriffs in Los Angeles County can typically count on being easily reelected in the primary, but Villanueva disrupted that pattern when he became one of only four challengers in the last century to push a sitting sheriff into a runoff. Political experts said this year's competitive race could signify a new era for the Sheriff's Department in which incumbents must fight to keep their jobs.