With ballots still being counted, an update Thursday showed Cisneros with a 941-vote lead, after Kim held an early edge in the contest.
Earlier Thursday, Democrat Katie Porter ousted Republican Rep. Mimi Walters in the 45th District in Orange County, a one-time Republican stronghold.
It was the fifth Republican-held House seat picked up by California Democrats.
With Porter’s win, Democrats will hold at least a 44-9 edge in California U.S. House seats.
Democrat Katie Porter captured a Republican-held U.S. House seat Thursday in the heart of what once was Southern California’s Reagan country, extending a rout of the state’s GOP House delegation that might not be over.
Porter’s upset in Orange County is a sign of changing times in a region once known nationally as a GOP fortress. The coastal county southeast of Los Angeles was home to President Richard Nixon, and President Ronald Reagan once likened it to a Republican heaven.
Porter, a law professor and protege of Massachusetts Democratic Sen. Elizabeth Warren, defeated Republican Rep. Mimi Walters, who was re-elected in a walkover just two years ago in the 45th District. The latest update to the vote count gave Porter 51 percent and a 6,203-vote lead.