Even so, he made no gains in Clinton's delegate lead, as each earned seven delegates as a result.
The Vermont senator was favored going into the caucuses. Wyoming is similar to other places he's won with big margins: rural, Western and overwhelmingly white. The victory is Sanders' eighth win out of the last nine contests -- including a contest that counted the votes of Democrats living abroad -- and a big morale booster heading into the crucial New York primary on April 19.
Sanders, speaking at a rally in Queens, New York, when the state's results were projected, announced the victory to his supporters after his wife, Jane, joined him on stage to say they had won.
"News bulletin: We just won Wyoming," Sanders said as the room exploded into cheers.
Sanders won 55.7% of the vote to Clinton's 44.3%, giving each candidate seven delegates. That helps Clinton maintain her pledged delegate lead over Sanders, 1,304 to 1,075.
A Clinton campaign aide said their "secret sauce" in Wyoming was the state's onerous vote-by-mail rules that required anyone voting by mail to have voted as a Democrat in the 2014 midterms.
"This is exactly the type of contest he needed to shut us out in," the aide said. "Not only did he not do that, he only netted two delegates, if that."
With 55% of remaining delegates in New York, Pennsylvania and California, one senior aide said "by the time we get to California, we will only need to meet threshold to win. He can win 85% and we're fine."
Sanders is banking on momentum to keep Clinton from officially clinching the nomination until the convention, when superdelegates will vote.
"If you look at the math, if you want to talk about math, the truth is is that it is very, very, very unlikely that either candidate, either Secretary Clinton or Sen. Sanders, will go into the convention with a majority needed of pledged delegates in order to win," Sanders campaign manager Jeff Weaver told CNN's Chris Cuomo on "New Day"
The Republican National Committee in a statement Saturday afternoon quickly noted Clinton's "embarrassing string of defeats," a sign, the RNC said, that Clinton will be beatable if she's the Democratic nominee.
Democrats turn out
Leaving nothing to chance, Sanders spent Tuesday night -- the evening he won Wisconsin's primary -- holding one of his signature large rallies in Laramie, a town of 30,000.
It could be all the attention Wyoming gets in the presidential contest. The rural, sparsely-populated state that's home to former Vice President Dick Cheney is solidly Republican
, so Democrats don't spend time trying to win it in the general election.
Saturday morning, Wyoming Democrats jammed into Cheyenne Central High School to caucus.
"We're expecting a record turnout throughout the state. There's a lot of excitement," said Aimee Van Cleave, executive director of the state Democratic Party. "It's wonderful today. Everyone will be allowed to vote. They're not being stopped by an early spring blizzard."
One group of enthusiastic Sanders partisans broke into a Bernie Sanders song to the tune of "Yankee Doodle Dandy."
"Elections in America are brought by corporations / Bernie is the only one who uses small donations," they sang, to the accompaniment of an acoustic guitar.
Republicans, meanwhile, are in neighboring Colorado
for a party convention where every delegate matters on the road to Cleveland's GOP convention and Donald Trump is trying to clinch the 1,237 delegates needed to win the nomination.
Keeping pace with Clinton
The Wyoming win could also help Sanders' impressive fundraising operation.
He has outraised Clinton, $109 million to $75 million, over the last three months, and wins along the way help him prime the small-dollar donor pump for the cash he'll need to compete in expensive, densely-populated East Coast media markets both in New York and the following week in Pennsylvania, Maryland, Connecticut, Delaware and Rhode Island.
The Democratic race has taken a sharply bitter turn in New York, where Sanders accused Clinton of "hustling money from the wealthy and powerful" on Thursday, and Clinton instructing Sanders: "Don't make promises you can't keep."
Sanders raised the stakes on Wednesday night, launching into a tirade on why Clinton is "not qualified" for the presidency by citing her positions on trade and her coziness with Wall Street interests.
"I'm not going to get beaten up. I'm not going to get lied about. We will fight back, but I do hope that we can raise the level and I do hope that the media will talk about real issues," he said Thursday in Philadelphia.
Clinton responded with a desire for unity -- to a point. She said that eventually, "we're going to have to unify Democrats," pointing to her own support for then-Sen. Barack Obama in 2008 after a hard-fought Democratic nominating contest.
Still, Clinton said she's going to "keep drawing contrasts" with Sanders.
"Because that's what elections are about," she said. "But I think it is important to tell people about what you're going to do for them, and how you can get it done -- how you can produce results that will make a positive difference in people's lives."