(CNN) -- When seven-term Republican Congresswoman Mary Bono Mack conceded to her Democratic challenger Raul Ruiz on Friday, she left two other members of California's GOP House delegation still trailing in tight, unsettled races.
As of Saturday, six of seven unresolved House races remain too close to call. In the seventh, two Louisiana Republicans will face off in a December 8 runoff for the 3rd District seat after none of the five candidates got the required 50%.
Democrats hold narrow leads in all six of the too-close-to-call races. Should all win, they will have picked up a net gain of eight seats in the House after losing the majority in the chamber and suffering the largest loss of seats since 1948 in the 2010 midterm elections.
Going into Tuesday's elections, Republicans held a 242-193 majority in the House.
Mack took over her seat after her husband Rep. Sonny Bono was killed in a skiing accident in 1998. In a heartfelt statement conceding defeat on Friday night, she congratulated her opponent, an emergency room physician, and thanked her family.
"Today, I called Dr. Ruiz and congratulated him on his impressive victory," Mack said. "Dr. Ruiz will do a fine job if he is guided as well by the people of the congressional district as I was. Please give him the opportunity to succeed.
"It was almost 15 years ago that Sonny died and I became a congresswoman," she continued. "Honestly, nobody worked harder or gave more since then than my two amazing children. They, along with my stepson Chaz, my grandson Sonny and my beloved husband Connie have been so supportive of me this week. I simply couldn't ask for more."
Mack lost by 4% of the vote or more than 7,200 ballots out of the almost 200,000 cast in the race for 36th District. The loss marks the first in her 14-year congressional career.
Her husband, former Rep. Connie Mack IV, also lost this week in his bid for U.S. Sen. Bill Nelson's seat in Florida.
Mack, who has faced redistricting twice before, once again saw her district's lines redrawn ahead of the 2012 election by a bipartisan commission in California based on 2010 census data.
The California delegation, which has been historically heavily Democrat, will send 36 Democrats and 15 Republicans to Washington as of Saturday, but that number could grow to 38 Democrats if the other two Republicans -- Rep. Dan Lungren and Rep. Brian Bilbray - are defeated.
Neither Lungren nor Bilbray have conceded, with provisional and absentee ballots still being recounted in both races.
Bilbray spokesman Patrick Howell said the race was "far from over," as additional ballots are processed. Bilbray trails Democrat Scott Peters by 1,334 votes in California's 52nd District.
Lungren trails his Democratic challenger Ami Bera by 1,779 votes as of Saturday. The race could drag on for weeks as Sacramento County election officials count the 98,464 vote-by-mail and 31,000 provisional ballots still outstanding.
Lungren's district is one of four in Sacramento County.
Another potential upset across the country could add yet another tick in the Democrats' tally.
Rep. Allen West rode the tea party wave to office in Florida's 18th Congressional District during the 2010 midterm elections, unseating three-term Democrat Rep. Ron Klein with more than an 8-point win. This time around, West faced a tough opponent in Republican-turned-Democrat Patrick Murphy.
But refusing to accept defeat after a vote count showed him down by 2,500 votes, West is demanding a full recount.
"There were numerous other disturbing irregularities reported at polls across St. Lucie County, including the doors to polling places being locked when the polls closed, in direct violation of Florida law, thereby preventing the public from witnessing the procedures used to tabulate results," a statement released by the West campaign said.
The West campaign filed injunctions against the supervisors of elections in Palm Beach County and St. Lucie County to impound voting machines and paper ballots.
"We will continue to fight to ensure every vote is counted properly and fairly, and accordingly will pursue all legal means necessary," the statement said.
The fiery tea partier isn't guaranteed a recount under Florida election law, which only stipulates an automatic recount in races if the margin of difference between the candidates is a half-percent or less. As close as the race is, it doesn't meet that criterion.
The West-Murphy contest is expected to be one of the most expensive congressional races in history, with the national parties and outside groups pouring money into the efforts. West raised significantly more than Murphy -- $17 million vs. $3.6 million.
Two races in Arizona also remain uncalled.
The contest for former Rep. Gabrielle Giffords' seat between Democrat Rep. Ron Barber and Republican Martha McSally finds Barber behind by 426 votes. Barber, former district director for Giffords, replaced her in a special election held after she was shot in the head and severely wounded in 2011.
The man convicted in the attack outside a supermarket that killed six people received a life prison sentence on Thursday.
And in a district across the state, Democrat Kyrsten Sinema is holding onto a 2,715-vote lead over Republican Vernon Parker while provisional and absentee votes are counted.
Parker might have Libertarian candidate Powell Gammill to blame if he does not win.
Gammill won more than 6% of the vote in Tuesday's election despite urging supporters to stay home rather than vote on Election Day in protest of the political system.
The unresolved contest in North Carolina could be the second tightest 2012 congressional race after provisional and absentee ballots are counted for the district that encompasses Wilmington and the area northwest to the Raleigh suburbs.
Democratic Rep. Mike McIntyre faced a tough re-election challenge. His district added Johnston County and his hometown of Lumberton was cut from the 7th District this year after redistricting.
Once the ballots are counted, either McIntyre or his Republican challenger and two-term state Sen. David Rouzer can request a recount if the margin remains a 1% or less. Both candidates have until November 20 to request a recount.
Gary Bartlett, the executive director for the State Board of Elections in North Carolina, said officials should know if Rouzer intends to request a recount before the November 20 deadline.
CNN Political Research Director Robert Yoon contributed to this report