Democratic congressional candidate Katie Porter jumped ahead of Rep. Mimi Walters, R-Irvine, for the first time Tuesday when updated tallies from last week's election were released by Orange County election officials.

The latest vote tally showed Porter leading Walters 50.1 percent to 49.9 percent, but Porter is ahead by just 261 votes.

Porter has made steady gains as vote-counting continued in the race for the 45th District seat. She was trailing Walters 51 percent to 49 percent as of last Thursday.

It was unclear exactly how many ballots still need to be tallied in the district.

Meanwhile, the race between Democratic philanthropist and veteran Gil Cisneros and Republican Young Kim was tightening in the 39th District, which straddles Los Angeles and Orange counties. The pair are vying to replace Kim's longtime boss, retiring Rep. Ed Royce, R-Brea.

According to the latest tally, which includes updated figures from both counties, Kim has 90,473 votes, or 50.2 percent, while Cisneros has 89,634, or 49.8 percent. Democratic real estate investor Harley Rouda, who declared victory on Saturday over incumbent Republican Rep. Dana Rohrabacher, had 52.2 percent of the vote, according to the latest tally.

In other close races, Democrat Cottie Petrie-Norris was leading Assemblyman Matthew Harper 51.1 percent to 48.9 percent.

Republican La Habra Mayor Tim Shaw was hanging on to a slim lead over Democratic Fullerton Mayor Doug Chaffee for the Fourth District Board of Supervisors race, with Shaw ahead 50.3 percent to 49.7 percent.