SACRAMENTO  (AP) — Republican Andy Vidak has a substantial lead in the hotly contested race for a San Joaquin Valley state Senate seat, with county election officials reporting Wednesday that nearly 9,500 ballots remain to be counted.

While tallying those ballots is expected to take until the end of the week, Democrat Leticia Perez ceded the contest late Wednesday.

"The voters have spoken and I want to congratulate Andy on his victory," Perez said in a statement.

Perez also had conceded the May primary to Vidak, only to learn she had earned a runoff when all the late ballots were tallied.

Vidak's campaign issued a statement in response, saying he looks forward to representing the district in Sacramento and to working with Perez, a Kern County supervisor.

Preliminary returns in the 16th Senate District show Vidak with 54 percent of the vote to Perez's 46 percent. The candidates are separated by about 5,800 votes.

To overtake Vidak, Perez would need to win roughly 80 percent of the outstanding ballots.

Fresno County election officials said they expect to report the updated tally on Friday. Officials in Kern, Kings and Tulare counties said they are aiming to have fresh totals sometime before the end of the week.

About 5,700 of the outstanding absentee and provisional ballots are in Fresno County, where returns slightly favored Perez. She also led in Kern, where 2,345 votes remain.

Vidak, a cherry farmer, held wide margins in his home county of Kings and in Tulare County, where a combined 1,433 ballots remain.

Democrats had hoped to hold the seat to protect their supermajority status in the Senate, prompting a flood of campaign contributions and a flurry of negative ads in both English and Spanish. Each campaign reported raising roughly $2 million.

If Vidak wins the seat, Senate Democrats will still maintain their two-thirds majority for this year. The party is expected to face several tough Senate contests in 2014.

The runoff came after Vidak won just shy of 50 percent of the vote in the primary. Perez received about 44 percent of the vote in that race, which featured two other Democratic candidates.

Perez conceded the primary before all the outstanding ballots had been counted, after preliminary returns showed Vidak with 52 percent. The Republican's margin dropped to 49.8 percent after absentee and provisional ballots were tallied, forcing the runoff.

The winner will replace Democrat Michael Rubio of Bakersfield, who resigned in February to work in the capital for Chevron Corp.

Democrats currently hold a voter registration advantage in the district — 51 percent to 31 percent — but the winner will have to run again next year in a reconfigured district that will be somewhat more favorable for Republicans.

Perez previously worked as an aide to Rubio and as an attorney in the Kern County Public Defender's Office.