For the first time in state history, voters in a Washington congressional contest will choose from two Republicans on the November ballot — leaving Democrats on the sidelines.

In Central Washington’s 4th District, former NFL player Clint Didier, a tea-party conservative, and former state agriculture director Dan Newhouse, topped the field of a dozen candidates seeking the seat left open by the retirement of 10-term Republican Congressman Doc Hastings.

Meanwhile, a potential surprise was brewing in the 1st Congressional District north of Seattle, where the Republican leadership’s hand-picked challenger, Pedro Celis, was in jeopardy of failing to make it through the primary against first-term U.S. Rep. Suzan DelBene, D-Medina.

Washington’s all-mail ballot system means thousands of votes will continue to trickle in and be counted in coming days. Ballots only had to be postmarked by election day.

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The historic result in the 4th District can be attributed to the state’s “top-two” primary system, which guarantees the top two voter-getters in the primary advance to November, regardless of party affiliation.

A matchup of two Republicans makes some political sense in the 4th District, a largely rural swath of farm country that includes Yakima and the Tri-Cities.

A Didier-Newhouse fight could pit the GOP’s tea-party wing against the establishment.

Newhouse, 59, a Yakima farmer who served as a state legislator and agriculture director under former Gov. Chris Gregoire, amassed the biggest campaign fund and endorsements from the Republican Party leaders.

Didier, 55, an Eltopia farmer who won two Super Bowl rings for Washington, D.C.’s team, relied on name recognition from previous statewide runs. He vowed to cut federal spending and to never raise taxes.

Democrat Estakio Beltran, a former aide to U.S. Sen. Maria Cantwell, split the Democratic vote with Yakima activist Tony Sandoval, leading neither to crack the top two in Tuesday’s returns.

In the 1st District, Celis was fighting for his electoral life Tuesday as returns put him in third place, behind Republican Robert Sutherland, a retired biochemist who reported raising $4,600.

Celis said Tuesday night it was hard to know what to make of the election results. “We’ll see what the numbers show tomorrow. I don’t want to speculate,” he said.

DelBene said her message will remain, saying voters want “folks who are going to work together across the aisles and find solutions.”

Celis, 55, a retired Microsoft software engineer,promoted his biography as a Mexican immigrant who has lived the American dream, while criticizing Dems on health care and the economy.

Like other Democrats, DelBene must contend with deep voter dissatisfaction with President Obama reflected in recent polls. But if Celis fails to advance past the primary, she may have a relatively easy path to re-election.

In 2012, DelBene spent $2.8 million of her own fortune to win the seat. A former Microsoft marketing vice president, DelBene so far this year has not spent her own cash but has raised nearly $1.8 million for her campaign, compared with about $430,000 for Celis.

In other state congressional races, incumbents easily advanced.

In the 7th District, Democratic U.S. Rep. Jim McDermott took more than three out of four votes counted Tuesday in his bid for a 14th term. A trio of little known challengers were battling for second place.

In the 9th District, U.S. Rep. Adam Smith, D-Bellevue, will face Republican Doug Basler this fall. U.S. Rep. Dave Reichert, R-Auburn, will face Democrat Jason Ritchie in the 8th District.

In Eastern Washington’s 5th District, U.S. Rep. Cathy McMorris Rodgers, the Spokane Republican, will be challenged this fall by Democrat Joe Pahkootas.

Jim Brunner: 206-515-5628