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.