A wealthy newcomer defeated the Democratic establishment’s pick for a redistricted House seat in the Washington suburbs Tuesday, the biggest victory in Maryland’s primaries.

In the closely watched Democratic primary, financier John K. Delaney beat state Senate Majority Leader Robert J. Garagiola (Montgomery) by a wide margin in a race that had been expected to be close.

Delaney will now face Rep. Roscoe G. Bartlett (R), whose district was redrawn to be tossup territory in November. Bartlett fended off state Sen. David Brinkley (Frederick) and six other Republican challengers in a battle for the night’s most contested seat.

Garagiola was the pick of much of the state Democratic Party establishment, which tailored the district lines to make them favorable to their candidate, while Delaney was a first-time candidate whose prodigious spending helped level the playing field. Delaney’s win was a repudiation of the party leaders and traditional Democratic interest groups that threw their weight behind Garagiola.

David Wasserman, the House editor for the nonpartisan Cook Political Report, blamed Garagiola’s loss in part on the fact that he chose not to go on the airwaves, while Delaney was a heavy presence on television and radio.

“Delaney’s win is confirmation you need a modern ad campaign to win a primary in the D.C. suburbs, where the cost of name recognition is steep,” Wasserman said. “It’s also confirmation that drawing the lines is no guarantee of electing a certain candidate.”

As former Massachusetts governor Mitt Romney won the state’s Republican presidential primary and Sen. Benjamin L. Cardin (D) easily beat back an intraparty challenge, all of the state’s eight U.S. House members won their primaries, and all but Bartlett appeared on track to win in the general election.

At the Potomac Community Center, Terry Ao said she supported Garagiola because she felt he echoed her social values.

“I am a civil rights attorney working for a nonprofit in D.C., and I felt that he spoke the most to my issues and concerns,” she said. Ao said she is particularly focused on the needs of the region’s “vulnerable communities” and felt that Garagiola “would be a champion for them.”

George Guess, 67, voted for Delaney. Guess said he was impressed by the strong grass-roots presence of Delaney’s campaign, with volunteers who came through neighborhoods to knock on doors.

“He struck me as close on the issues to Garagiola, but Delaney was endorsed by [former president Bill] Clinton, and he had all those guys on the ground rather than just calling,” Guess said. “I thought that was more sensitive to the people, less canned.”

At Hillcrest Elementary School in Frederick, Henry Brown, 71, said he voted for Delaney because, “If it’s good for Bill Clinton, it’s good for me.”

Turnout across the state appeared to be “relatively light,” said Donna Duncan, a spokeswoman for the Maryland State Board of Elections.

“We’ll be lucky if we reach 25 percent” of registered voters, she said, a level which would roughly match turnout in the state’s 2004 primaries.

The story of Delaney and Garagiola’s months-long fight followed an unusual arc.

When Annapolis Democrats redrew the state’s congressional map, they decided to target Bartlett by adding the western portion of Democratic-leaning Montgomery County to the more conservative Maryland panhandle. And at the urging of state Senate President Thomas V. Mike Miller Jr. (Calvert), a close Garagiola ally, they drew the 6th Congressional District to include Garagiola’s Germantown home but exclude those of several other prominent Montgomery Democrats.

U.S. House Minority Whip Steny H. Hoyer (D-Md.) threw his weight behind Garagiola, as did every major union and such liberal groups as MoveOn.org and the League of Conservation Voters. Maryland Gov. Martin O’Malley (D) also endorsed Garagiola in the closing days of the race.

But Delaney, the founder of the Chevy Chase commercial lender CapitalSource, was able to leverage some of his own political connections, winning the backing of Clinton as well as Comptroller Peter Franchot and Rep. Donna F. Edwards of Prince George’s County.

Delaney raised roughly double what Garagiola did in the first quarter of the year from outside donors, and Delaney also put about $1.7 million of his own money into his campaign. He ran a host of television and radio ads, while Garagiola was silent on the airwaves.

The tenor of the race was often negative. Delaney branded Garagiola an Annapolis “insider” and criticized him for not reporting outside income from a lobbying job on state disclosure forms. Garagiola accused Delaney’s business of unsavory practices and pointed out his contribution to the congressional campaign of Rep. Andy Harris (R-Md.) in 2010.

Bartlett, meanwhile, was leading a field that included Brinkley and Del. Kathy Afzali (Frederick). Although the redrawn district includes territory he has never represented, and some state Republicans had privately expected him to retire, Bartlett appeared to benefit from the fact that the anti-incumbent primary vote was split several ways.

At Potomac United Methodist Church, Republican Roger Thies said he supported Bartlett because he felt he was the GOP’s best bet at retaining control of the competitive seat.

“Clearly the Democrats have tried to gerrymander [the district], and I think Bartlett has the best chance to hold it, on name recognition alone,” Thies said. He said it was the “sole reason” he cast his ballot for Bartlett.

In the Senate contest, Cardin easily deflected a primary challenge from state Sen. C. Anthony Muse (Prince George’s) and seven other Democrats. With roughly a quarter of the precincts reporting, Cardin led Muse by more than 50 percentage points and had been declared the winner by The Associated Press.

“We are extremely pleased by our results in all parts of the state,” Cardin said in a brief interview. “We’re ready for the general.”

Muse, who is black, made the case that Prince George’s needed a better voice in Congress and pointed out that the Senate has no African Americans. But Cardin, who won an early endorsement from President Obama, was better known around the state and far better funded than Muse.

Walking out of the polling site at Bethesda-Chevy Chase High School, Don Allen said he voted for Cardin. Although he said he thinks there should be more African Americans in Congress, he thought Muse — who opposes same-sex marriage — “was too far to the right on social issues.”

Cardin is also favored in November against the eventual Republican nominee, particularly with Obama atop the ballot. Former Secret Service agent Daniel Bongino led ex-Defense Department official Richard Douglas in a tight race to face Cardin.

On the House front, author Ken Timmerman was the Republican pick to take on Rep. Chris Van Hollen (D). Republican activist Faith Loudon prevailed in the contest to face Edwards, while Del. Anthony J. O’Donnell (Calvert) won the GOP nod to oppose Hoyer.