Representative Adam Schiff, the lead prosecutor in Donald J. Trump’s first impeachment trial, and Steve Garvey, a former Major League Baseball star, advanced on Tuesday night to the California general election for a Senate seat, according to The Associated Press.

Election night returns showed that Mr. Schiff, a longtime Democratic congressman from the Los Angeles area, and Mr. Garvey, a Republican political novice, had secured two spots on the November ballot ahead of Representative Katie Porter, an Orange County Democrat who had been their closest rival.

Representative Barbara Lee, a Democrat and well-known Bay Area progressive, was in fourth place.

The November general election will determine who will replace Dianne Feinstein, who held the seat for more than three decades until her death in September.

During the campaign, Ms. Porter, 50, had accused Mr. Schiff, 63, and his supporters of engineering Mr. Garvey’s ascendance to set up an easier November election. Mr. Schiff, who had raised more than $30 million by last month, spent lavishly on statewide ads that compared Mr. Garvey to Mr. Trump, and that framed him as Mr. Schiff’s chief opponent.

The strategy encouraged the state’s Republican voters to consolidate behind Mr. Garvey, 75, who is still recognized from his days playing for the Los Angeles Dodgers and San Diego Padres more than three decades ago. And it elevated Mr. Schiff as the leading Democrat for an electorate dominated by liberals.

The two candidates are now set up for a fall race in which the electoral math will be overwhelmingly in Mr. Schiff’s favor. Democrats have a 2-to-1 voter registration advantage in California, and the state has not elected a Republican to statewide office since Arnold Schwarzenegger was re-elected as governor in 2006.