Sen. Lisa Murkowski (R-Alaska) conceded her primary race Tuesday night, becoming the third senator to lose renomination this year and the second to lose a primary.

Murkowski called a halt to her bid after failing to close the gap on lawyer Joe Miller after two-thirds of the 25,000 absentee votes were counted Tuesday. She gained barely any ground on Miller and remained about 1,600 votes short of winning her party's nomination.

"It's been a long week," Murkowski told reporters at her campaign headquarters in Anchorage. "I don't see a scenario where we could win."

Miller moves into a general election as a strong favorite to succeed Murkowski. He faces underfunded Sitka Mayor Scott McAdams. A GOP poll this week showed Miller leading McAdams, 52 percent to 36 percent.

Murkowski joins Sen. Arlen Specter (D-Pa.) in losing a primary this year. Sen. Robert F. Bennett (R-Utah) fell at his party's May convention.

In addition, four House incumbents have lost their primaries.

The Alaska result also represents the latest victory of a "tea party" candidate over candidates backed by GOP leaders, after similar outcomes in Nevada, Kentucky, Colorado and Utah.

The little-known and badly outspent Miller was endorsed by former Alaska governor Sarah Palin (R), a tea party heroine.

Jennifer Duffy, a Senate campaign analyst for the nonpartisan Cook Political Report, told Bloomberg News that Murkowski didn't take Miller's candidacy seriously enough.

Although Murkowski raised 20 times as much money as Miller, she was reluctant to run negative political ads.

"When you know this is an election cycle that does not favor incumbents, you take absolutely nothing for granted, and I think Murkowski took a lot for granted," Duffy said.

The Tea Party Express political action committee poured money into advertising and e-mail blasts for Miller, who criticized Murkowski for her support of the 2008 federal government bank bailout. The group spent more than $400,000 on such independent expenditures for the race this month, reports to the Federal Election Commission show.

Staff writer Aaron Blake contributed to this report.