With about 55 percent of the expected vote counted in unofficial results, Murray claimed first place with about 46 percent of the vote. Rossi took the second spot with about 34 percent.
Washingtons unusual primary lists all candidates on a single ballot and winnows the field to two for the general election, regardless of the candidates party. Conservative Republican Clint Didier, a former NFL tight end who attracted support from tea party activists, was in third place with about 12 percent of the vote.
Murray enjoyed a primary-day visit from President Barack Obama, part of the presidents national tour to help Democratic candidates.
In his first visit to the state as president, Obama headlined two fundraising events for Murray and the state Democratic Party. The expected haul was estimated at about $1.3 million.
At a Seattle hotel, Obama told a packed fundraising luncheon that the country needs Patty.
I can tell you we would not have been able to get some of the critical things we got done this year had it not been for her leadership. So make sure you send her back to Washington, please, Obama said.
Rossi, who has campaigned mainly against federal spending and the national debt, declared that he would put Washington, D.C., on a pork-free diet.
People understand that were spending too much money, Rossi said. They know that you cant keep borrowing from the Chinese and Saudis and printing money and expect all that to pan out just fine, because it wont.
Nearly all of Washingtons 3.6 million voters use absentee ballots, with only one county still offering traditional polling places. Ballots were mailed statewide in late July and must be postmarked or dropped off by Tuesday.
Rossi was heavily recruited by national Republican officials to challenge Murray, who has regularly polled below 50 percent in this campaign. Rossi finally announced his campaign in late May, just days before the deadline for registering as a candidate.
Since then hes sought to turn one of Murrays chief strengths, the ability to deliver federal money, into a liability.
Murray has not run from her record of bringing federal spending to the state, pointing out jobs that were bankrolled by such efforts and warning that a freshman senator who decries earmarks would simply surrender that money to other states.
Brian Kenny, 37, of Seattle, said he was supporting Murray because he likes the Democratic agenda thats been advanced since Obama took office.
I supported health care reform, financial reform and energy reform. I think Rossi would obstruct that. I dont see viable solutions from the right, Kenny said.
Matt Martin, 42, of Kenmore, was among those protesting outside Obamas first fundraiser for Murray. Holding a sign that said Pork Patty with a drawing of a pig with Murrays likeness, Martin said hed supported Didier but was mostly motivated to defeat Murray.
Im going to vote for the conservative candidate, whichever one it is, in the actual election, he said.