A huge late-campaign TV ad blitz pushed Democrat Suzan DelBene into the November election in the hotly contested 1st Congressional District, ending fellow Democrat Darcy Burner's third bid for Congress.

In initial returns Tuesday, John Koster, the only Republican in the seven-way race, overwhelmed the field to grab 44 percent of the vote and a spot in the top-two primary.

In a six-way race for the other place on the Nov. 6 ballot, DelBene, with 23 percent, was handily beating Burner by nearly 9 points. Burner called DelBene to concede.

DelBene, before supporters in Kirkland, congratulated Koster but said Democrats would unify against him.

"We all agree on one thing: We all need to keep this congressional district blue," she said.

Setting a campaign theme, she called Koster "a tea-party Republican" who is "far too extreme for the people of the 1st District, and for Washington."

Koster, at his South Everett headquarters, scoffed at the labels: "I'm just gonna be who I am. The message is still the same," he said. "They call it extreme. I think they're extreme."

DelBene set a state record for self-financing in a congressional race with $2.3 million. That supplied a line of attack for Burner, who reversed a pledge not to criticize fellow Democrats when she blasted DelBene in a late-campaign flier.

The 1st District, which stretches from Redmond to Canada, was the state's most-contested congressional race, with nearly $5 million raised overall. And it was by far the most unusual.

After Democratic Rep. Jay Inslee vacated the seat to run for governor, Gov. Chris Gregoire called a special election to fill a one-month vacancy in December.

Democratic and Republican Party officials tried to discourage the regular-election candidates from also running in the special election, to avoid voter confusion. But when Burner jumped in at the last minute, all but two candidates followed.

In the special election, Koster and DelBene were leading.

The race had other sour flavors. The mother of Democratic candidate Laura Ruderman spent at least $215,000 on a PAC that attacked DelBene's business record, calling her "Suzan DelRomney."

Burner, a favorite of progressive activists, drew attention in the campaign by calling for women to "cast off the shame and embarrassment" of abortion and for telling the NRA "to go to hell."

"We did everything we could, but it's difficult when you get outspent the way we were," said Burner at her campaign party in Redmond. Democrats must make sure "that Suzan wins in November."

The five Democrats held similar liberal positions on social issues. State Sen. Steve Hobbs, a fiscal moderate, diverged on some economic and labor issues. He was fifth in ballot counts, behind Ruderman.

DelBene, a former Microsoft vice president and state revenue director, advocates tighter Wall Street regulations and higher taxes on the wealthy, including herself.

Koster, a longtime Snohomish County Council member and former state lawmaker, holds strong fiscal and social conservative views, calling for comprehensive tax and immigration reform.

National political handicappers rate the 1st District as leaning Democrat. The state redistricting commission redrew the boundaries last year to be a 50-50 "swing" electorate that supported both President Obama in 2008 and Republican Dino Rossi in the 2010 Senate race.

Staff reporters Susan Kelleher, Connor Radnovich and Lornet Turnbull contributed. Jonathan Martin: 206-464-2605 or jmartin@seattletimes.com. On Twitter @jmartin206.