NYC Mayor-elect Michael Bloomberg is flanked by Mayor Rudy Giuliani and N.Y. Gov. George Pataki at his acceptance speech Wednesday morning.

By Manuel Perez-Rivas
CNN Washington Bureau

NEW YORK (CNN) -- Republican Michael Bloomberg defeated Democrat Mark Green in Tuesday's mayoral election, cresting late in a ferocious race after receiving the endorsement of exiting GOP Mayor Rudolph Giuliani.

Green, a liberal who had often been at odds with Giuliani,conceded the race early Wednesday morning, saying: "We gave it our all, but it wasn't enough."

"This was a very tough, close race," Bloomberg told campaign supporters gathered for his acceptance speech. "But the good news is, we have won."

Bloomberg then invited Green and Democrats to "join with us to make this city better."

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Green had been the early frontrunner in the heavily Democratic city, but the late endorsement from the popular Giuliani, who could not run again because of term limits, helped propel Bloomberg in the last days of the campaign.

Bloomberg, the billionaire head of a large media firm, is estimated to have poured more than $50 million of his own money into the race -- a record for a municipal election -- blitzing the city with campaign ads for months. Yet his campaign crested sharply only after he received the Giuliani endorsement.

Meanwhile, Green -- the city's public advocate-- was hurt by a divisive Democratic runoff against Bronx Borough President Fernando Ferrer, who was bidding to become the city's first Hispanic mayor. Exit polls Tuesday showed that Latino voters split their support between the two candidates, though they have historically voted with the Democrats in New York.

Much of the race in recent weeks focused on which candidate would best be able to take up Giuliani's mantle, and rebuild a downtown financial district shattered by the Sept. 11 collapse of the World Trade Center's twin 110-story towers, which housed tens of thousands of jobs, and hundreds of thousands of square feet of prime office space.

Green sought to portray Bloomberg as a political novice who lacked the know-how and the experience to lead the city in its time of post terror-attack crisis.

Bloomberg countered that his experience atop his media empire qualified him to occupy the mayor's office at City Hall, and to lead the nation's largest city. And he cited his lack of political experience to cast himself as an outsider who was not beholden to the city's political machine.

"I think that my experience through building a company and managing people through economically trying times, providing leadership to 8,000 employees and 200,000 customers, makes me qualified to lead this city," he said.

Despite his millions, Bloomberg had a huge obstacle to overcome in the city's voting rolls, where just one out of five registered voters is a Republican. It's an obstacle only a handful of Republicans -- including Giuliani -- have been able to overcome in a city dominated by Democrats for more than a century.

With his victory, though, Bloomberg will face a series of challenges more difficult than the arduous campaign.

In addition to rebuilding Manhattan and trying to fill Giuliani's oversized shoes, the new mayor will take the reins of a city beset by mounting budget deficits and pressing needs in schools, housing, transportation and other key areas.