Former Los Angeles Dodgers player Steve Garvey continues to ascend in the polls leading up to California’s March 5 primary for an open Senate seat with the latest poll placing him in a statistical tie with Democratic Congressman Adam Schiff.

A poll by Berkeley Institute of Governmental Studies published March 1 shows the Republican garnering 27 percent of likely voters, and Mr. Schiff receiving 25 percent of the likely vote. Democratic Congresswoman Katie Porter came in third with 19 percent, followed by Rep. Barbara Lee, also a Democrat, who claimed 8 percent, among a crowded field of candidates running for the seat left vacant after the death of longtime Sen. Dianne Feinstein in September.

The large increase in voter support for Mr. Garvey over the past six weeks occurred by the consolidation of Republican and conservative voters, 67 percent of whom now back the candidate, according to Mark DiCamillo, director of the poll.

“A big part of Garvey’s appeal to primary election voters relates to voter perceptions that he will be tougher on the nation’s immigration problem than the other candidates,” Mr. DiCamillo said in a press release Friday.

Nearly 94 percent of Mr. Garvey’s supporters, in the poll, said his immigration stance was very important to them in deciding whom to support in the race, according to Mr. DiCamillo.

If Mr. Garvey wins the seat, he would become the first California Republican to serve in the Senate since Sen. Jon Seymour left in 1992.

Mr. Seymour was appointed in 1991 by Gov. Pete Wilson, who resigned his seat after being elected governor in 1990. He lost to Ms. Feinstein in the 1992 special election to determine who would serve the remaining term.

Candidates of all parties compete in California’s primary March 5. Regarding the senate seat, voters will first be asked which candidate they would choose to serve a full six-year term. A second vote will be for a candidate to complete the remainder of Ms. Feinstein’s term, which ends in January 2025.

The top two candidates with the most votes in the primary will move forward to the state’s general election in November.

If the latest poll numbers hold true, Mr. Garvey and Mr. Schiff would compete Nov. 5. Likely voters, however, favor Mr. Schiff by a large margin if that happens, according to the poll, preferring him by 15 points.

Voter support for Mr. Garvey was even stronger in the race to serve the final few months of Ms. Feinstein’s term. In that race, he was the leader, receiving 29 percent of likely voters, while Mr. Schiff and Ms. Porter trailed at 23 percent and 20 percent, respectively, according to the poll.

Friday’s poll findings showed a substantial shift in support for Mr. Garvey. A January poll, also by the Berkeley Institute of Governmental Studies, showed Mr. Schiff at 21 percent, Ms. Porter at 17 percent, and Mr. Garvey at 13 percent.

(L-R) Rep. Adam Schiff in Los Angeles on May 26, 2023. (Jerod Harris/Getty Images for Demand Justice); Rep. Katie Porter in Washington on April 18, 2023. (Tasos Katopodis/Getty Images for Patriotic Millionaires); Rep. Barbara Lee in Oakland, Calif., on May 21, 2023. (Kimberly White/Getty Images for Demand Justice); Former Dodgers baseball player Steve Garvey in Los Angeles on October 7, 2013. (Stephen Dunn/Getty Images)

The candidates have since faced off in two public debates, during which Mr. Schiff tied the former first baseman to former President Donald Trump, saying Mr. Trump was the “gravest threat” the country faced to its democracy. Mr. Garvey’s backers, however, cited his support of the former president as a main reason to vote for him, poll results showed.

Next Tuesday’s primary is shaping up to have an historically low turnout.

Of California’s 22 million registered voters, only 2.5 million vote-by-mail ballots were returned by Thursday, according to election officials.

Democratic voters in the state account for nearly 47 percent of voters, compared to 24 percent who have registered as Republicans, according to data released Friday by the California Secretary of State.

“Garvey is the chief beneficiary in a low turnout election scenario, as he holds a huge advantage over the field among fellow Republicans and both he and Schiff are the two most preferred candidates among older voters, whites, and homeowners,” Mr. DiCamillo said.

Regionally, Mr. Garvey holds the lead among voters in Orange County, the Inland Empire, San Diego County, and the Central Valley, according to the poll. Mr. Schiff leads in Los Angeles County, the San Francisco Bay Area, and the Central Coast.

Those who support Mr. Schiff say he would be a strong voice in defending abortion rights and is a strong opponent of Mr. Trump.