UPDATE 11:48 p.m

Vermont U.S. Sen. Bernie Sanders scored a stunning victory over Hillary Clinton in Hawaii Democrats’ presidential preference poll Saturday, mobilizing a grass-roots campaign that signed up thousands of new Democrats and defied the wishes of almost the entire “old guard” of the party.

The Sanders victory in Hawaii capped a three-state sweep Saturday that showed his campaign continues to mount an unexpectedly potent alternative to former Secretary of State Clinton’s presidential bid. Sanders was also victorious in Washington and Alaska.

A number of Hawaii residents complained the party’s voting was cut off too early, leaving dozens of people who arrived late standing around in school parking lots without an opportunity to participate. Party officials had announced the polling would start at 1 p.m. but never explained when the voting would end, which caused confusion.

Sanders dominated the race with 70 percent of the vote to Clinton’s 30 percent, with all precincts counted. Turnout was expected to be strong and did not disappoint with 33,716 votes cast.

Sanders won 17 delegates and Clinton received eight, according to the final tally. The delegate tally does not include nine so-called Hawaii superdelegates, most of whom support Clinton.

In a statement issued after the preliminary results showed a lopsided victory, Sanders said, “I want to thank the people of Hawaii for their strong support and for turning out in huge numbers for Saturday’s caucuses. Nobody should have any doubt that this campaign has extraordinary momentum and that we have a path toward victory. In state after state, our grassroots effort has taken on the entire political establishment.”

Almost all of Hawaii’s Democratic establishment had endorsed Clinton, including former Govs. George Ariyoshi, Ben Cayetano and John Waihee, U.S. Sens. Brian Schatz and Mazie Hirono, former U.S. Sen. Daniel Akaka and U.S. Rep. Mark Takai, among others.

The Sanders campaign countered by sending a half-dozen professional campaign staffers to Hawaii to organize telephone banks and an online voter registration push that targeted younger voters, where Sanders has strong appeal.

Democratic Party officials reported 7,000 new members have signed up since late last year, and most of those new members are believed to be Sanders supporters.

Bart Dame, authorized representative for the Sanders campaign, predicted even before the vote was announced that Saturday’s balloting would represent an important psychological victory for the Sanders camp.

“The national Clinton campaign, aided by many media outlets, are trying to say that Sanders should fold his tent and accept defeat and rally behind Clinton, but those of us active in the campaign believe that is premature, and that’s a form of psychological warfare,” Dame said. “We believe that Bernie still has a chance to win.”

As the date for the Hawaii voting approached, both campaigns rolled out slick direct-mail pieces and professional television advertising, with Sanders’ ads featuring popular U.S. Rep. Tulsi Gabbard.

Friends Aaron Toyama, 28, and Robert Young, 28, showed up at Highlands Intermediate School in Pearl City to vote for Sanders because they support his social policies. Toyama, a machinist and Pearl City resident, added that Sanders fights for the middle class.

“He’s been for the people since he started in office,” said Toyama, who sported a Sanders “A Future to Believe In” pin on his shirt.

Graham Watt, a Pacific Palisades resident and information technologist, said he was not surprised by the high turnout at Highlands Intermediate, where he cast a vote for Clinton.

“While I appreciate that Bernie Sanders is … energizing the discussion, I’m not with it because I’m not sure how he will implement it,” said Watt, 47. “(Clinton) is a bit more to the middle. She is more of a moderate.”

The Clinton campaign focused more on coaxing existing, mainstream party members to turn out for voting than on signing up new members. The Hawaii Government Employees Association and United Public Workers unions endorsed Clinton and were helpful in mobilizing party members to vote, according to Clinton campaign volunteer Ember Shinn.

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Star-Advertiser reporter Jayna Omaye, Dan Nakaso and Michael Tsai contributed to this report.