Hillary Clinton claimed a narrow victory in Kentucky as she sought to put away Bernie Sanders, but her resilient rival for the Democratic presidential nomination bounced back to snatch a win in Oregon.
With the Kentucky race too close for most US networks to call a winner, Clinton declared victory shortly after Kentucky's secretary of state Alison Lundergan Grimes announced on CNN that Clinton was the unofficial winner in her state.
"We just won Kentucky! Thanks to everyone who turned out," Clinton tweeted.
With 99.8 percent of Blue Grass state precincts reporting, Clinton led Sanders by 46.8 percent to 46.3 percent -- a margin of less than 2,000 votes.
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Should the results hold, the win would blunt Sanders's momentum and help Clinton move closer toward clinching the Democratic presidential nomination.
But the psychological win was short-lived. Half an hour after polls closed in Oregon, US networks projected Sanders the winner there, besting Clinton 53 percent to 47 percent.
"We just won Oregon, and we're going to win California," Sanders told thousands of supporters in Carson, California as he predicted victory in the nation's largest state, which votes on June 7.
Sanders, a self-declared democratic socialist, declared he would not be forced out of the race by narrow Clinton wins.
"It appears tonight that we're going to end up with about half the delegates" in Kentucky, Sanders told the raucous rally.
"Let me be as clear as I can be... We are in 'til the last ballot is cast," he said to a huge roar.
Clinton has a commanding lead in the all-important national delegate count and is marching toward vying for the presidency in the November 8 general election despite her string of recent primary losses.
Victories in Kentucky and Oregon would have definitively halted her slide and helped reverse the narrative that her campaign is showing significant weakness ahead of an almost certain showdown with Donald Trump, the Republican Party's presumptive nominee.
Trump -- the last man standing in the GOP race -- was projected Oregon's Republican winner, moving closer to the 1,237 delegates he needs to officially claim the party's mantle in 2016.
Sanders had counted on a Kentucky victory to build on his win last week in neighboring West Virginia as he battles to keep his long-shot nomination bid alive.
West Virginia and Kentucky are linked to coal, as is much of Appalachia -- the largely white, long-struggling eastern US region where many feel they have been left behind in the lukewarm recovery from the 2007-2008 financial crisis.
Clinton saw Kentucky as an opportunity to appeal to working-class white men -- a demographic where the former secretary of state has lagged behind both the celebrity billionaire Trump and Sanders.
John Spenlau, 28, speaking to AFP outside a voting station in Louisville, said he voted for Sanders because he represented the best hope for "continued change" and the fight against income inequality, among other problems.
"Hillary would be a more stable candidate but I think that Bernie continues to push the envelope, towards a few more of the social programs that I believe in," Spenlau said.
- Closing the deal -
Clinton defeated Barack Obama in Kentucky's primary in 2008, and her husband Bill Clinton was the last Democrat to carry the Bluegrass State in a general election.
Republicans were gleeful over her inability to close out the Democratic nomination race against Sanders, who at the beginning of the campaign was given long odds against the better-funded, universally recognizable former first lady.
"While Republicans move toward unifying the party for the general election, Hillary Clinton remains bogged down in a nasty, protracted primary fight and will have to rely on a rigged system of superdelegates to get across the finish line," said Reince Priebus, chairman of the Republican National Committee, in a statement
On Sunday, playing up her husband's popularity, the former first lady appeared to indicate Bill would play a role in her administration if she were elected, promising to put him "in charge of revitalizing the economy." She later said she would not give him a cabinet position.
As voting got underway, Trump fired off a series of nasty tweets at Clinton.
"Crooked Hillary can't close the deal with Bernie Sanders. Will be another bad day for her!" Trump wrote.
The Clintons have struggled to contain the damage from comments Hillary made in March, when she said she vowed to put many coal miners "out of business" in the transition to cleaner energy.
In recent appearances she has struck a more inclusive tone, and it may have helped her squeak by in Kentucky.
"We need to take coal country, coal miners and their families with us and not leave them behind," Clinton told supporters on Monday.
Clinton, 68, barnstormed Kentucky on Sunday and Monday, shaking hands, taking selfies, offering hugs -- even chatting with Trump supporters at a smoke-filled diner in the southwestern city of Paducah.
"I will not vote for you. I will never vote for you," disabled veteran Dianna Dooley, 66, told her.
Clinton kept her composure, saying: "That's OK. You vote for whoever you want."