House Democrats realized one of the largest net gains of anywhere in the country in the Mid-Atlantic region Tuesday night, picking up at least five and possibly six GOP-held seats.

The final margin rests in the balance because the open-seat contest in Maryland’s 1st district still had not been called as of press time Wednesday. Democrats were ahead in the contest, but only by a very slight margin.

There were few surprises in New Jersey, where every incumbent held on to his seat. House Democrats had high hopes for picking up two open seats in the Garden State — in the swing 3rd and 7th districts — but the party was able to win only one.

Democratic state Sen. John Adler won the 3rd district and will take the seat being vacated by Rep. Jim Saxton (R), who is retiring after 13 terms in the House. Adler, who jumped into the race before Saxton announced his retirement, defeated Medford Mayor Chris Myers (R).

In the 7th district, state Senate Minority Leader Leonard Lance (R) prevailed over state Assemblywoman Linda Stender (D). Democrats viewed this open seat as one of their best chances for a pickup when Stender chose to run again after losing to retiring Rep. Mike Ferguson (R) by just 1 point in 2006. But this year, she faced a much bigger defeat as Lance cruised to a 9-point win.

In New York, Democrats picked up three seats, including those of retiring GOP Reps. Vito Fossella and Jim Walsh.

Fossella saw his hopes for re-election slip away after he was charged with drunken driving earlier this year. He was the last Republican to represent a New York City seat and he will be succeeded by Democrat Michael McMahon, who defeated Republican Bob Straniere.

The GOP lost another seat in the Empire State when retired Navy officer Eric Massa (D) ousted Rep. Randy Kuhl (R) in a battle for his Rochester-area seat. The two also faced off in 2006, when Kuhl, who has served two terms, won by a mere 2 points. With 99 percent of the precincts reporting, Massa won this time, also by 2 points.

In one bright spot, Republicans held the seat of retiring Rep. Tom Reynolds, a former two-term chairman of the National Republican Congressional Committee. Businessman Chris Lee handily defeated Alice Kryzan to win the 26th district seat. Only three Republicans will return to the New York delegation in the 111th Congress.

Over in the Keystone State, Rep. Phil English (R) was ousted. The seven-term Congressman lost to businesswoman Kathy Dahlkemper (D) in a race that national Democrats targeted. In previous elections, English, who presents himself as a moderate, has faced little competition for his seat, but Dahlkemper’s campaign strategy of running as a business-savvy outsider helped her oust the GOP lawmaker.

Rep. Paul Kanjorski, considered one of the most vulnerable Democrats in the House heading into Election Day, managed to hold onto his seat in Pennsylvania’s 11th district. He defeated Hazleton Mayor Lou Barletta (R), who gained national attention because of his stances on illegal immigration.

Kanjorski appeared to be in peril when a SurveyUSA poll taken Oct. 30-Nov. 2 for Roll Call showed Barletta leading 51 percent to 45 percent, mirroring other public surveys. Kanjorski has been dogged by ethical concerns and had only a 35 percent approval rating among respondents. Despite that, the Democrat managed to squeak out a 4-point win.

Rep. Christopher Carney (D), who defeated Republican Chris Hackett, may have held onto his seat in Pennsylvania’s 10th district by distancing himself from the Democratic Party. The district elected Carney to a second term without him ever using the word “Democrat” in an ad and without his endorsement of President-elect Obama. Carney sailed to victory with 56 percent of the vote to Hackett’s 44 percent.

In Delaware, Sen. Joseph Biden (D) easily won a seventh Senate term but he is now headed to the other end of Pennsylvania Avenue as vice president-elect.

The question is: Who will replace him?

The task of picking a successor falls on the shoulders of outgoing Gov. Ruth Ann Minner (D), though it is possible Gov.-elect Jack Markell (D) will be tasked with the decision. There has long been speculation that Biden would like to be succeeded by his son Beau Biden, who gained fame after delivering an impassioned speech at the Democratic National Convention in August. There has also been conjecture that Minner would appoint herself, though she has said she will not.

Complicating matters is the fact that Beau Biden, the state attorney general, is a military reservist who is deployed in Iraq and is not expected to return to the United States until later next year.