Billionaire Michael Bloomberg won a third term as New York mayor Tuesday in a closer-than-expected race against a Democratic challenger who stoked voter resentment over the way Bloomberg changed term-limits law so he could stay in office.

With 99 percent of precincts reporting, Bloomberg, the richest man in New York and founder of the financial information company Bloomberg LP, defeated William Thompson Jr. 51 percent to 46 percent.

In the days leading up to the election, polls showed Bloomberg with as much as an 18-point lead, an edge so big that critics accused the mayor of overkill in his strategy of bombarding the city with campaign ads.

His margin of victory was far smaller than the nearly 20-point blowout he pulled off in 2005.

At a victory rally with supporters, Bloomberg lauded Thompson for running "a spirited campaign."

"We will get our city through these tough times," he promised. "We'll come out stronger than ever."

More than $100 million spent
When all the bills are paid, Bloomberg will probably have spent more than $100 million on his campaign, the most expensive self-financed campaign in U.S. history. Thompson, the city's comptroller, relied on donations and matching funds for his mayoral bid, and was on track to have spent about a tenth of Bloomberg's staggering total.

Thompson ran up huge margins in black and Hispanic neighborhoods, winning by a 3-to-1 margin in some districts.

He beat Bloomberg handily in predominantly black neighborhoods like Bedford-Stuyvesant in Brooklyn and Jamaica in Queens. He won Harlem and East Harlem easily, along with other heavily Hispanic districts in upper Manhattan and the Bronx.