LOS ANGELES (AP) — Several Democrats gained ground Friday against Republican incumbents in closely contested U.S. House races in California, where votes continue to be counted.

Fifteen-term U.S. Rep. Dana Rohrabacher fell farther behind Democrat Harley Rouda, a real estate executive, in Orange County's coastal 48th District. Rouda extended his lead to 7,300 votes, or nearly 52 percent, returns showed.

In the neighboring 45th District, Democrat Katie Porter inched closer to Republican U.S. Rep. Mimi Walters, whose lead shrank to 2,020 votes, or 1 percentage point, out of about 205,000 ballots tallied. Two days earlier, she led by about 6,000 votes.

And in the Central Valley's 10th District, Democrat Josh Harder grabbed a nearly 2-point lead after trailing Rep. Jeff Denham.

In retiring GOP Rep. Ed Royce's 39th District, the race was also tightening. Republican Young Kim held about a 2,600-vote edge over Democrat Gil Cisneros, or 2 points, with about 164,000 votes counted. If elected, Kim would become the first Korean-American immigrant woman elected to the House. At midweek, she had a 3-point edge.

Tens of thousands of provisional and late-arriving mail-in ballots remain to be counted in each district.

Like Royce, Rohrabacher and Walters represent districts in Orange County, a one-time Republican stronghold where Democrats are attempting to capture as many as four GOP-held districts. They already have won one — retiring U.S. Rep. Darrell Issa's seat went to Mike Levin, a former Orange County Democratic Party official.

And Democrats also have picked up the last Republican-held House seat anchored in Los Angeles County. First-time candidate Katie Hill, 31, ousted Republican Steve Knight, who was seeking a third term in the 25th District in northern Los Angeles County and a slice of Ventura County.

Hill's victory gave Democrats a 40-13 advantage in California's congressional delegation.

The Republican-turned-Democrat Rouda has depicted Rohrabacher as the face of gridlock on Capitol Hill. Rohrabacher, first elected as a Reagan Republican, had been campaigning as a maverick willing to buck both parties.

Porter is a law professor and a protégé of Massachusetts Democratic Sen. Elizabeth Warren.

Denham, known for his involvement in water issues vital to agriculture, has proven tough to beat, despite the Democratic registration edge in the 10th District. But after taking a 1,300-vote lead on Election Day, he fell behind Harder by 3,200 votes on Friday, when about a third of the 174,000 votes were counted.

Harder says Republican policies in Washington have hurt many residents in a region known as the state's fruit-and-nut basket.

Hill stressed her centrist politics: She's a gun owner, and her Republican father is a police officer who had never voted for a Democrat before her primary. Her mother, a Democrat, is a nurse.

Hill, who worked as an executive for a group providing services for the homeless, supports universal health care and counts Massachusetts Sen. Elizabeth Warren, a liberal favorite, among her supporters. But she also highlighted her family's military service and says immigration policy must start with securing the nation's borders, echoing a familiar Republican refrain.

Her endorsements run from firefighters to unions to Equality California, an LGBT advocacy organization. Hill is married and openly bisexual.