Republican Dino Rossi conceded defeat to Sen. Patty Murray on Thursday evening in the hotly contested Washington Senate race.

He called the three-term Democrat and offered his congratulations, according to a statement from his campaign.

“I ran for the Senate because I believe we need a basic course correction from where Washington, D.C. has been taking us and to make sure this country is as free, as strong and as prosperous in the future as it has been in the past to preserve the best of America for future generations,” he said in the statement. “That was a message that found a very receptive audience all across this state, though not quite receptive enough.”

Rossi’s concession came after the Seattle Times reported Thursday evening that Murray’s lead was virtually insurmountable, even though hundreds of thousands of ballots had yet to be counted. Rossi would have needed to get 54 percent of the almost 600,000 votes that had yet to be counted to overcome Murray’s lead, according to an analysis done by the Seattle paper.

According to the state’s latest tally, Murray now has a 45,000-vote lead over Rossi. That lead has steadily grown since Election Day, when Murray led by just 14,000.

A large portion of the outstanding ballots are from King County, where Murray already has a large lead. Washington votes entirely by mail, so the process of counting remaining ballots is expected to take weeks.

Murray’s victory means that only two Democratic Senate incumbents were defeated in the 2010 midterms: Sens. Russ Feingold of Wisconsin and Blanche Lincoln of Arkansas. It also means that the net Republican gain in the Senate remains unchanged at six seats.