As Shannon P. O’Brien struggled to maintain a razor-thin lead in the Massachusetts gubernatorial campaign, she and other state Democrats celebrated with a Scottish pipe band at a Cambridge hotel on Friday night.

Rep. Michael E. Capuano (D-Mass.), whose Eighth District spans Cambridge, Somerville and part of Boston, hosted a party for O’Brien and hundreds of supporters at the Royal Sonesta Hotel.

“The fact that we are one point in the lead is terrific news,” O’Brien said from the stage of the gilded meeting room, where the campaign posters of more than 20 different candidates—some of whom also took the stage—lined the walls as guests wandered among buffet tables and two drink bars.

The mood among Democratic faithful was optimistic but focused.

“Every one of us has been in the political system for a long time,” Capuano told guests at the beginning of the event. “You know what it takes. You know what we’ve got to do.”

Capuano recalled Ralph Nader’s 2000 presidential campaign and stressed the need to convert potential Green Party voters to O’Brien’s side so as to gain extra support in the close race against Republican W. Mitt Romney.

About 7 percent of likely voters intend to vote for Green Party candidate Jill E. Stein ’73, according to recent polls.

“It’s not time to waste the vote. We lost the presidency before,” Capuano said.

Guest Lou Ann David, a Somerville resident, agreed.

“I love the Green Party,” David said. “But we can’t win this alone, and Mitt is not our guy.”

O’Brien was upbeat, joking to applause and cheers that she dressed as “Mitt Romney’s worst nightmare” for Halloween.

“We’re going to work hard and we’re going to break our hump to get Shannon elected,” promised Capuano, who is running uncontested for election to his third congressional term.

Capuano urged the Harvard community to participate in the election.

“Get out and vote,” he said. “It matters because my son’s at Harvard and I’m only paying for half of his education. The rest comes from government.”

Reggae, contemporary pop and forties hits filled the hall between speeches.

Such a “combination of political party and party party” is known as a “time” within the political community, said Daniel A. Schlozman ’03, chair of the Cambridge Ward Eight Democratic Committee.

Some of the guests relished the catered buffet and thumping music as much as the chance to hobnob with political doyens.

George Thomas, an elderly guest dressed in a light suit and carrying a metal cane, smiled impishly under a pale cap and bounced his hips back and forth to a disco beat as he traced circles around the room.

Another man wearing a stars-and-stripes top hat with a matching tie, handkerchief and ribbon wandered through the crowd clutching a drink.

Though all of the guests were strong supporters of the Democratic contenders, some did not agree with the candidates’ approach to campaigning.

Mark D. Trachtenberg, a librarian who is running as a Ninth District candidate for the Boston City Council, criticized O’Brien’s campaign strategy.

“It’s all too easy for the strength of her record to get overlooked with all the mudslinging between the candidates,” he said.

In her brief speech, O’Brien mentioned problems that have arisen under Massachusetts’ past three Republican governors, but Mary Louise Daly, formerly a librarian at MIT, said the O’Brien campaign should have raised this point sooner.

“Someone dropped the ball,” she said.

Yet signs of guests’ enthusiasm for the Democratic candidates echoed from every corner of the room.

The Bunker Hill Pipe Band paraded into the room between speeches to the rhythmic clapping of the enthusiastic crowd.

A large man in a white sweater put furry white mallets to a large drum as the bagpipers droned “I’m a Yankee Doodle Dandy” in kilts.

A woman twirled her scarf and danced to “American Pie” as the party drew to a close.

Richard Girolamo, a Somerville resident, who first knew the party’s host politically when Capuano was the mayor of Somerville, became nostalgic in the wake of the evening’s political fervor, impressed by Capuano’s own political accomplishments.

“One night I couldn’t sleep and I turned on C-SPAN and I saw Mike Capuano speaking and I said, ‘Jesus, that’s great,’” he said. “You get a little pang in your heart.”