With about 60 percent of precincts reporting, Republican Andy Vidak had about 54 percent to Democrat Leticia Perez's 46 percent. They are competing to fill a vacancy in the 16th Senate District that opened when Democrat Michael Rubio resigned earlier this year.
Democrats are hoping to hold the seat to protect their supermajority status, prompting a flood of candidate campaign contributions and independent expenditures. Each side reported roughly $2 million in donations.
Despite the intense fundraising and political implications, light turnout was expected. In the May primary, 22 percent of voters cast a ballot.
Vidak's campaign consultant, Tim Orman, said shortly after polls closed that vote-by-mail ballots favored the Republican.
"It's very encouraging at this point," Orman said.
Vidak, a cherry farmer, won just shy of 50 percent of the vote in the May primary, sparking the runoff against Perez, a Kern County supervisor. She received about 44 percent of the vote in the primary, with two other Democrats in the race.
The district includes all of Kings County and portions of Fresno, Kern and Tulare counties.
In Tuesday's other special legislative election, independent Paul Leon, the former mayor of Ontario, was leading a field that also included one Republican and seven Democrats. With nearly 88 percent of precincts reporting, it appeared no candidate would garner more than 50 percent of the vote, triggering a Sept. 24 runoff.
The nine candidates are competing to succeed Democrat Norma Torres, who resigned her 52nd Assembly District seat when she was elected to the state Senate. The heavily Democratic district covers parts of Los Angeles and San Bernardino counties.