BOSTON -- Boston Mayor Thomas Menino was elected to an unprecedented fifth term as the city's mayor on Tuesday, defeating challenger Michael Flaherty.

"The stories may say that today we beat our toughest opponent, but we haven't passed the biggest obstacle yet -- complacency is the highest hurdle we face. Let's fend off the temptation to rest on past accomplishments or to walk in familiar paths," Menino said during his victory speech.

Menino, who has already has been in office for 16 1/2 years -- longer than any mayor in the city's history, did not hint at whether this would be his last run. Sources said Flaherty is already looking ahead to a rematch.

"I'm going to stay involved. I had a brief conversation with the mayor tonight, and I congratulated him and I asked him if he would be willing to do this in four years," Flaherty said.

"I said, 'Good fight, Michael. I enjoyed it, and lets get together in the near future,'" Menino said.

Flaherty had run in an unusual partnership with City Councilor Sam Yoon. Flaherty, a lifelong resident of South Boston, had vowed to make Yoon, a community organizer of Korean descent, his deputy mayor had won.

Menino said this race has been the toughest of his political career because he had multiple opponents.

"I had four opponents, really. I had Councilor Flaherty, Councilor Yoon, Kevin MacRae and the Local 718 Firefighters Union. They spent a million-and-a-half dollars trying to defeat me," Menino said earlier on Tuesday.

Locked in a bitter contract dispute with Menino, Boston firefighters urged voters to cast their ballots for Flaherty.

"You need new blood, new ideas up there. The school systems are a mess; they need to be fixed. Public safety is a mess," said Boston firefighter Bill Murphy.

"What we're looking forward to is a new beginning for Boston and getting away from the old vindictive schools of management," said Boston Firefighter Union President Ed Kelly.

Menino was one of nearly two dozen incumbent mayors facing challenges on Election Day in Massachusetts.

Another one of the more heated races was in Quincy, where Mayor Thomas Koch beat out former Mayor William Phelan in a rematch of their 2007 race.

Brockton made history Tuesday by electing Linda M. Balzotti as its first female mayor. In Newton, Setti Warren was elected mayor over Ruth Balser. In Lawrence, Rep. William Lantigua defeated City Council David Abdoo, becoming the first Latino to be elected mayor in state history.

In Springfield, Mayor Domenic Sarno was re-elected.

In North Adams, John Barrett -- the state's longest serving mayor -- is seeking a 14th term against Richard Alcombright.

New mayors are being chosen on Tuesday in Agawam, Fall River, Holyoke and Newburyport, all cities where incumbents were either not running or were ousted by in preliminary elections.