Democrats bested Republicans in California’s senatorial primary and most of the state’s 52 congressional contests on Super Tuesday.

Republicans, though outnumbered two-to-one in registered voters, managed to hold their ground by winning several congressional primaries that the Democratic National Committee (DNC) had targeted to flip in 2024.

In California’s open or “jungle” primary system, the top two finishers in each race—regardless of party—advance to the general election. That sets up a head-to-head rematch between the leading contenders in November.

Here’s a breakdown of the races we’re watching closely.

Senate

Democrat congressman Adam Schiff defeated Republican Steve Garvey in the Senate primary, claiming 38 percent of the vote to Mr. Garvey’s 28 percent.

November’s election will mark the first time in three election cycles that a Republican candidate has advanced to the general election.

Democrat congresswoman Katie Porter placed third with 15 percent. Democrat congresswoman Barbara Lee garnered 7 percent.

The March 5 election was unusual in that voters had the opportunity to vote for a senator twice, once in the primary election for a full, six-year Senate term and once in a special election to fill the remainder of the late Sen. Dianne Feinstein’s term. Ms. Feinstein, a Democrat, held the seat from 1993 until her death last September.

The results for the special election primary were nearly identical to the regular primary total. Mr. Schiff and Mr. Garvey will face off in both contests on November 5.

District 22

Incumbent Republican David Valadao appears poised to win in District 22, one of eight California seats the DNC hopes to flip in 2024.

Mr. Valadao was several percentage points ahead of Democrat Rudy Salas late on March 5, setting up a November rematch between the two. Mr. Valadao also fended off a challenge on the right from Trump-aligned Republican Chris Mathys.

Mr. Valadao narrowly defeated Mr. Salas to win the seat in 2020, claiming 51 percent of the vote.

Some 42 percent of registered voters are Democrats and just under 27 percent are Republicans in this district, which the Cook Political Report calls a toss-up.

District 27

Incumbent Republican Mike Garcia received 52 percent of the vote in District 27, another seat targeted for reversal by the DNC.

Democrat George Whitesides received 34 percent of the vote and will face off against Mr. Garcia in November. Mr. Whitesides is a former chief of staff at NASA and former CEO of Virgin Galactic.

Both campaigns have raised over $3 million. Cook Political Report lists the contest as a toss-up.

District 13

In a rematch of the second tightest congressional race in the nation in 2022, incumbent Republican Rep. John Duarte edged out Democrat challenger Adam Gray in California’s 13th congressional district.

As the only two candidates in the race, the pair will face off again in November in a match that could decide which party controls the House of Representatives.

District 47

Republican Scott Baugh held a slight lead in District 47 late on March 5, in the race for the seat vacated by Democrat Katie Porter, who is running for the U.S. Senate.

Democrat state Sen. Dave Min trailed by less than 1 percent in this district, which encompasses Irvine, Costa Mesa, Huntington Beach, Newport Beach, Sunset Beach, Seal Beach, and South Laguna.

Mr. Baugh, a business attorney, former chairman of the Orange County Republican Party, and state assembly leader, was one of three Republicans in the race. He will face Mr. Min again in the November election.

In the 2022 general election, Ms. Porter narrowly defeated Mr. Baugh with 51.7 percent of the vote.

District 9

Incumbent Democrat Josh Harder won in District 9, which the RNC hopes to flip in November.

Mr. Harder collected 55 percent of the vote over the Republican mayor of Stockton, Kevin Lincoln, who won 27 percent.

The district, which encompasses Stockton, Lodi, Tracy, and Manteca, is listed as “likely Democrat” by the Cook Political Report.

District 49

Democrat incumbent Mike Levin defeated four Republican contenders in District 49, another seat the RNC hopes to flip, claiming 52 percent of the vote.

Republican Matt Gunderson, a car dealership owner, garnered 24 percent of the vote and will join Mr. Levin on the November ballot.

Republican Margarita Williamson received 11 percent of the vote.

This Southern California district, listed as “likely Democratic” by the Cook Political Report, takes in the beach cities of Solana Beach, Encinitas, Carlsbad, and Oceanside in San Diego County, as well as San Clemente, Dana Point, and Laguna Niguel in Orange County.

District 20

Republican state assemblyman Vince Fong is positioned to claim the top spot in District 20, the seat recently vacated by former Republican House Speaker Kevin McCarthy.

Mr. Fong, who gained the endorsement of former President Donald Trump, held 38 percent of the vote late on March 5 over Democrat Marissa Wood, who held 24 percent.

Republican challenger Mike Bourdeaux, the sheriff of Tulare County, had attempted to secure the MAGA vote in this solidly red district. He was poised to finish third with 23 percent of the vote.

District 40

In District 40, Republican incumbent Young Kim took the top spot with 51 percent of the vote, facing off against a pair of Democrat challengers. Joe Kerr, a fire captain with the Orange County Fire Authority and president of the Orange County Professional Firefighters Association, received 30 percent of the vote, while Allyson Damikolas, an engineer and Tustin Unified School District trustee, received 19 percent.

Ms. Kim and Ms. Damikolas will advance to the general election in November.

The historically red district takes in Yorba Linda, Chino Hills, Orange, and Tustin.

In the 2022, general election Kim defeated Democrat Asif Mahmood with 56.8 percent of the vote in the district, which is rated  “likely Republican” by the Cook Political Report.

District 41

In District 41, Republican incumbent Ken Calvert, one of the most senior members of Congress, leads the race with 46 percent of the vote over Democrat challenger Will Rollins, who has 45 percent.

The district includes Corona, Menifee, Lake Elsinore, Temescal Valley, Palm Springs, and Palm Desert.

Mr. Calvert defeated Mr. Rollins by more than 11,000 votes in the 2022 general election, claiming 52.3 percent of the total.

District 45

Republican incumbent Michelle Steel defeated four Democrats in District 45, which is located in the traditionally red northern Orange County, claiming 51 percent of the votes.

The results disappointed Democrats who had hoped to flip the seat in 2024.

Democrat challenger Derek Tran received 19 percent of the votes, and Kim Nguyen-Penaloza received 16 percent.