The former secretary of state fended off a fierce challenge from Vermont Sen. Bernie Sanders, who has captured the energy and enthusiasm of younger Democratic voters.
Clinton's win was powered by strong turnout among minority voters and a well-organized machine in populous Clark County, where she was beating Sanders 52.5% to 47.4% with 87% of the vote counted.
"I am so thrilled and so grateful to all my supporters out there," Clinton said as she took the stage at her victory rally in a ballroom at Caesar's Palace, giving a special thank you to hotel and casino workers "who never wavered."
"Some may have doubted us but we never doubted each other, and this one is for you," she said.
Clinton struck a populist tone as she sought to channel the anger of voters against big banks and corporations, which Sanders has so skillfully harnessed.
"Let me say this to the men and women who run our country's corporations: If you cheat your employees, exploit consumers, pollute our environment or rip off taxpayers, we are going to hold you accountable," Clinton said.
She also subtly knocked Sanders' agenda as unachievable: "Americans are right to be angry but we are also hungry for real solutions."
Wrapping up the rally, Clinton told her supporters she was headed to the upcoming primary state of Texas while her husband was headed to Colorado.
"The fight goes on!" Clinton said as the room erupted into cheers.
Sanders, for his part, complimented Clinton on an "aggressive, effective campaign" in Nevada in his nine-minute concession speech.
But he added that, "Five weeks ago we were 25 points behind in the polls. We've made some real progress."
He struck an upbeat tone and signaled that he was looking beyond South Carolina -- where Clinton is expected to win -- to the Super Tuesday states.
"We are going to be taking on a very well funded superPAC," he said. "On Super Tuesday, we would very much like the support of the American people. We have received over 3.7 million in individual contributions," he added, directing supporters to go to his website to help with additional contributions. "Taking on the establishment, the financial establishment, the political establishment, the media establishment is not easy. We have come a very long way in 9 months. It's clear to me that the wind is at our backs, we have the momentum," he said to cheers.
Nevada Democratic Party spokesman Stewart Boss estimated turnout at 80,000, falling short of the nearly 120,000 voters who turned out in 2008.
A win by Sanders, who trounced Clinton in the New Hampshire primary, would have dealt Clinton a dramatic setback. The victory was a huge relief for Clinton and her allies, who were clearly rattled by what appeared to be an unexpectedly tight race here in a state that was long viewed as her firewall.
Beyond name recognition, Clinton had enormous organizational advantages over Sanders -- not least of which was the fact that she began organizing some six months before the Vermont senator.
In a wild final week where Nevada polls showed Sanders pulling even with the former first lady, Clinton's campaign pumped an additional half-million into its advertising buy on cable, broadcast and satellite -- bringing her to parity with Sanders on the air, though she was already far better known than her rival.
Clinton also engaged in a furious campaign push in populous Southern Nevada, leaving nothing to chance even in the final hours before voters lined up to caucus.
In the days before the caucuses, she far outpaced Sanders on the campaign trail with a series of stops on the Las Vegas Strip to appeal to shift workers, visits to labor- and immigration-focused events and even a surprise stop at a Las Vegas caucus site Saturday.
One key to her victory: though the powerful Culinary Workers Union here stayed neutral, Clinton made an ardent push to win over their members (the union endorsed Barack Obama in 2008). She made an overnight visit to meet with the housekeeping staff at Caesar's Palace, stopped at a uniform department at one of the casinos and repeatedly went to casino employee dining rooms to make personal appeals to workers.
Those efforts clearly paid off: She posted a strong performance at the six caucus locations that were set up for shift workers on the Las Vegas strip. Minority voters, who tilted Clinton's way, turned out in strong numbers -- only about six in 10 caucus-goers were white according to exit polls.
"She is the best person to help everybody -- on immigration, and with the children," said 55-year-old Ofelia Sanchec, a Caesar's Palace housekeeping worker as she stood in line Saturday waiting to caucus for Clinton with fellow employees. "She is a lady, the first woman president. I hope she will help us."
Asked whether she considered Sanders, Sanchec said no: "For me, I know Hillary."
Repeating the pattern of Iowa and New Hampshire, Nevada exit polls showed that younger voters tilted heavily toward Sanders. The Vermont Senator carried more than 8 in 10 voters under 30, while Clinton carried two-thirds of those 45 and older.
But for some of those younger voters, like 29-year-old Vanessa McCallum, Saturday's decision was difficult down to the final moments, when she had to decide whether to sit on the Sanders or Clinton side of the caucus at Caesar's Palace.
"It's a heart versus logic thing," said McCallum, a Las Vegas massage therapist who ultimately caucused for Clinton. "I love Bernie Sanders. And I love him because he's the only candidate who is enticing everybody -- the youth vote -- to get up, get out and do something. I respect his policies. I respect him as a person."
In the end, McCallum said, she questioned what Sanders would be able to achieve. Voters across America, she said, "are scared of the whole democratic socialist thing."
"I've always been curious to know how is he going to guarantee that his next four years wouldn't be a repeat of Obama and his struggles of the first four years with everybody filibustering everything that he does," McCallum said.
As she sat down with the Clinton contingent inside the caucus, she covered her eyes and said she felt like she was "cheating on Bernie," but that logic had won out.
Clinton relied on strong turnout from Latino voters to hold Sanders at bay. Her surrogates fanned out across the Silver State this week, attempting to portray her as the more trustworthy candidate for Latinos.
In the final days, Clinton's allies slashed Sanders' immigration record, criticizing him as a "Johnny-come-lately" to the issue who has been too vague about his plans.
At the same time, in Nevada's rural counties Clinton's canvassers pressed the case that Sanders' proposals are unrealistic and unachievable in the current political climate.
Sanders emphasized his family's immigrant roots here in ads and on the campaign trail, noting that his father came to America from Poland and originally spoke little English.
"Immigration isn't just a word for Bernie Sanders," the narrator said in one Spanish-language radio ad for his campaign in November. "His story is the immigrant story."
But Clinton promised to make an immigration overhaul part of her agenda in her first 100 days.
On Thursday, the same day that her campaign put an additional half million into their ad buy, Clinton released an emotional immigration ad featuring the candidate talking to a tearful 10-year-old girl about the deportation letter that her parents received.
"I'm going to do everything I can so you don't have to be scared," she told the young girl in the ad, her arm wrapped around her. "Let me do the worrying. I'll do all the worrying. Is that a deal?"
Meeting with workers, the former secretary of state stressed that she understood their struggles.
"I know you do a hard job," she told Caesar's Palace housekeeping workers during that overnight visit to their linen room on Thursday after flying into Las Vegas from Chicago. She said that when she arrived at the hotel, she had asked herself: "Who is still working?"
"A lot of people are," she said, before asking the workers to caucus for her.