Hillary Clinton found herself in an unexpected battle for the support of primary voters in Nevada, as Bernie Sanders and Martin O’Malley impressed at a caucus dinner in Las Vegas on Wednesday night.

The Nevada caucuses, scheduled for 20 February, are the third primary to take placee, making the state crucial for a candidate hoping to build momentum.

In front of a raucous crowd of 2,200 people armed with yellow plastic vuvuzelas, hand-pumped red squeak-horns and flashing blue air traffic control sticks, the three candidates set out their core policy areas rather than addressing each other directly. Rather they reserved their ammunition for Donald Trump.

Sanders’ supporters were by far the noisiest and most vocally enthusiastic from long before the candidates emerged. Chants of “Bernie! Bernie!” went up several times before general cheers drowned them out. A small coterie held aloft a rainbow H for Hillary, but as Born in the USA played the candidates in, the chants of Sanders’ supporters drowned out the others.

Bernie Sanders speaks in Las Vegas. Photograph: Mikayla Whitmore/AP

That support could signal a problem for Clinton in a state which she had previously thought relatively safe, a stronghold even. Sanders only hired a state director for Nevada in October, while the Clinton campaign has had staff in place since April.

Clinton still maintains a commanding lead in the polls, but signs are emerging that she may not be in as strong a position in the state as she would like. Politico reported on Wednesday that Erin Bilbray, once one of her most loyal supporters in the Nevada Democratic party, had endorsed the Vermont senator.

Despite languishing far behind both Clinton and Sanders in the polls, Martin O’Malley gave a barnstorming speech that impressed many in the room with its concrete policy proposals, and won growing applause among an audience largely – and audibly – made up of die-hard Clinton and Sanders supporters.

“My experience is different from my competitors,” O’Malley said. “My experience is as an executive, a mayor and a governor. Getting things done. Actions, not words.” He pointed out that under his governorship, Maryland had been the first state in the union to introduce a living wage, and that he had also passed a climate change bill, the Dream Act, marriage equality legislation and eliminated the death penalty. “These were actions not words,” he said.

Sloan Hickson, a first-time voter from Henderson, Nevada, said he had come to the dinner with his mother, a Clinton supporter, to see what the different options were.

“O’Malley surprised me,” he said. “I wasn’t expecting anything, because I hadn’t heard much about him. But when he went up and started going, a lot of people I was sitting with really liked him.”

Katrina Brown, a union electrician from north Las Vegas, said that she had also been impressed by O’Malley’s speech, and that he had come across as “someone who gets things done”. But “I’m working class, so Bernie resonated the most,” she said.

Clinton used her speech to hit out at the Republicans and set out her stall as the most likely candidate to win the general election in November. “In January 2017 a new president is going to walk into the Oval Office,” she said. “And America can’t afford for it to be a Republican, who will rip away all the progress we’ve made.”

In a dig at Sanders, she said Americans deserved “a president who can get the job done … and not just on a few issues, but on all the problems we face”.

“If the Republicans aren’t worried about me, then why are hedge fund billionaires already running ads against me?” she asked. “Why are the Koch brothers?”

Sanders struck back at Clinton, albeit obliquely, in a speech that otherwise strayed little from his usual core theme of income inequality and social justice. “Let me be very clear and be a little bit political here. All of us want to make sure that we defeat rightwing extremism, that we make certain that no Republican becomes president,” he said. “But let me be very clear. That result will not happen with establishment politics and establishment economics.”

The gulf between the Sanders and Clinton support was very visible. While the one spoke, the other’s supporters sat in near silence, Clinton’s camp stage right, Sanders’ stage left.

Among the less-committed, the evening was generally encouraging. “I think that whoever wins [the nomination], we’ll be OK,” Brown said.