The state’s congressional races drew intense interest from national Democrats and Republicans alike this year, after California’s independent redistricting process transformed them from gerrymandered strongholds to free-for-alls in which once-safe, long-serving lawmakers fought for their political lives.

In one of the newly drawn districts in the rural San Joaquin Valley, early returns showed freshman Republican Rep. Jeff Denham staving off his Democratic challenger, former NASA astronaut Jose Hernandez.

The district, split evenly between Democrats and Republicans, attracted more than $8 million from political action committees and other outside groups, making it the nation’s seventh-most expensive in terms of outside spending.

Democratic Reps. John Garamendi and Jerry McNerney in the Central Valley and Lois Capps in Santa Barbara, as well as their GOP colleagues Reps. Brian Bilbray of San Diego and Mary Bono Mack of Palm Springs, also held narrow leads, early returns showed.

One exception was Democratic Rep. Pete Stark, the longest-serving member of California’s largest-in-the-nation congressional delegation, who early returns showed was trailing behind his challenger, fellow Democrat and Dublin City Councilman Eric Swalwell.

Some of the most negative election battles this year pitted candidates from the same party against one another, thanks to California’s new top-two primary.

Democratic House members Rep. Brad Sherman and Rep. Howard Berman pitched a battle over a single San Fernando Valley seat that even got physical when Sherman roughly grabbed the smaller Berman by the shoulder during a debate, pulled him toward his chest and hollered, “You want to get into this?”

The two major parties reported raising and spending millions in California on 2012 but kept a keen eye on the 2014 midterm elections, when Democrats believe they stand a good chance at retaking a majority.

The state’s delegation is 33 Democrats and 19 Republicans, with the seat of former Democratic Rep. Dennis Cardoza up for grabs next year after he resigned in August when the fall ballot was already set.

The desert communities near Palm Springs became one of the hottest battlegrounds, where Rep. Bono Mack sought to fend off Harvard-educated physician Raul Ruiz, an effective Democratic fundraiser adept at mobilizing the district’s growing swath of Hispanic voters.

The race typified the influence of money and the negative tone in many congressional races this year.

Last week, Ruiz got major cash infusions from the Democratic Party’s congressional arm and a super PAC founded by the son of liberal billionaire George Soros, after being hit with a barrage of attack ads from Bono Mack highlighting his participation in a 1997 Thanksgiving Day protest at Plymouth Rock in which several Native American activists were arrested. Ruiz was never charged in the incident.

Bono Mack, an eight-term congresswoman who co-chairs Mitt Romney’s California team, called her opponent “un-American” for failing to discuss his involvement early on. She acknowledged the race had been her most competitive since she was elected in 1998 to fill the seat of her late husband, entertainer Sonny Bono.

“This candidate is willing to say anything to any group of people in order to get them to side with him,” she said in an interview.

Ruiz’s campaign, in turn, highlighted an email in which Mack referred to part of her district as a “third world toilet.”

“We have enormous differences and disparities in income and job availability and education here,” he said in an interview. “It’s unfortunate that Congresswoman Bono Mack does not want to talk about what is really important.”

Democrats and Republicans also have been dueling in tight races in several congressional districts surrounding Sacramento.

San Diego’s 52nd district, where Republican Rep. Brian Bilbray is trying to fend off Democratic challenger Scott Peters, also was considered a tossup.

As of Tuesday, outside groups had spent nearly $8.3 million on the race, making it the nation’s sixth-most expensive in terms of outside spending. By comparison, the campaigns together had spent $4.1 million through Sept. 30, the most recent figures available.

All told, super PACs and other outside groups flooded California’s House races with more money than any other state under new rules allowing unrestricted outside political spending . By Tuesday, spending had reached nearly $54 million, according to the Center for Responsive Politics.