Bloomberg had pressed ahead with plans to run the marathon on schedule, but opposition intensified quickly Friday afternoon from the city comptroller, the Manhattan borough president and sanitation workers unhappy that they had volunteered to help storm victims but were assigned to the race instead.
Finally, about three hours later, the mayor relented.
"We would not want a cloud to hang over the race or its participants, and so we have decided to cancel it," Bloomberg said in a statement. "We cannot allow a controversy over an athletic event even one as meaningful as this to distract attention away from all the critically important work that is being done to recover from the storm and get our city back on track."
City and race officials considered several alternatives: a modified course, postponement or an elite runners-only race. But they decided cancellation was the best option.
Organizers will donate various items that had been brought in for the race to relief efforts, from food, blankets and portable toilets to generators already set up on Staten Island.
The cancellation means there won't be another NYC Marathon until next year.
"I understand why it cannot be held under the current circumstances," Meb Keflezighi, the 2009 men's champion and a former Olympic silver medalist, said in a statement. "Any inconveniences the cancellation causes me or the thousands of runners who trained and traveled for this race pales in comparison to the challenges faced by people in NYC and its vicinity."
Bloomberg called the marathon an "integral part of New York City's life for 40 years" and "an event tens of thousands of New Yorkers participate in and millions more watch."
He still insisted that holding the race would not have required diverting resources from the recovery effort. But he said he understood the level of friction.
"It is clear it that it has become the source of controversy and division," Bloomberg said. "The marathon has always brought our city together and inspired us with stories of courage and determination.
Bloomberg's decision came just a day after he appealed to the grit and resiliency of New Yorkers, saying, "This city is a city where we have to go on."
The nationally televised race winds through the city's five boroughs and has been held annually since 1970, including 2001, about two months after the 9/11 terrorist attacks.
Mary Wittenberg, president of the organizing New York Road Runners, said it was the right move to cancel.
"This is what we need to do and the right thing at this time," she said.
"It's been a week where we worked very closely with the mayor's office and felt very strongly, both of us together, that on Tuesday it seemed that the best thing for New York on Sunday would be moving forward. As the days went on, just today it got to the point where that was no longer the case."
Wittenberg said she sensed an animosity toward runners in general as the week wore on. About 10,000 runners were expected to drop out after the storm arrived, she said.
Howard Wolfson, deputy mayor for government affairs and communications, said the mayor's office consulted with officials in all levels of government during the week. There was no one tipping point, he said.
Wolfson acknowledged that local businesses won't take in all of the $340 million the marathon was estimated to attract. But because many runners had already traveled to the city, money will still pour in.
Wittenberg said the relief fund announced Thursday had already raised $2.6 million.
Patrick Lynch, president of the Patrolmen's Benevolent Association the police department's largest union called the decision to cancel the marathon "a wise choice."
ING, the financial company that is the title sponsor of the marathon, said it supported the decision to cancel. The firm's charitable giving arm has made a $500,000 contribution to help with relief and recovery efforts, and is matching employee donations.
As of now, NYRR is sticking to its policy of no refunds for the runners, but will guarantee entry to next year's marathon. But Wittenberg said that stance will be reviewed.
Eric Jones said he was part of a group from the Netherlands that collected $1.5 million to donate to a children's cancer charity if the runners competed.
"We understand, but maybe the decision could have been made earlier, before we traveled this far," said Jones, whose group came to New York a day earlier.
Steve Brune, a Manhattan entrepreneur, was set to run his fourth NYC Marathon.
"I'm disappointed, but I can understand why it's more important to use our resources for those who have lost a lot," he said.
Brune said he thinks foreign runners who traveled for the race will be even more disappointed.
"When you have a significant amount of people voicing real pain and unhappiness over its running, you have to hear that. You have to take that into consideration," Wolfson said.
"Something that is such a celebration of the best of New York can't become divisive. That is not good for the city now as we try to complete our recovery effort, and it is not good for the marathon in the long run," he said.
Earlier in the day, race preparations seemed under way as normal.
White tents where the runners would meet were already erected. Plastic crates lined the park's wall for two blocks, with tangles of electric wires and other setup equipment where workers buzzed around. A few TV news crews set up camp.
Along the race route in Queens, a couple of marathon banners hung from street lamps.
"I'm not a fan of what he's doing," Manhattan resident Michael Folickman said of Bloomberg's decision. "I think that if the bridge is cleared and the streets are clear, I don't think it'll wreak any more havoc than what's already been wreaked."
"And I think it could be an uplifting experience for the city to have something exciting like that happen on top of this terrible hurricane," he said.
In Brooklyn, the effects of the storm were more apparent. One gas station had a long line of cars extending down the block. Another had dozens of people standing on the sidewalk, clutching red fuel cans.
In Staten Island, Eddie Kleydman said ruined neighborhoods like his are still waiting for help.
"Look at this," he said, motioning toward the huge piles of discarded furniture and household items that line his street. "Who cares about the marathon? We need garbage trucks, we need FEMA to act quicker. He's worried about the marathon; I'm worried about getting power.
"So he called it off. He has to come here and help us clean," Kleydman said.
At the midtown New Yorker Hotel, the lobby was filled with anguished runners, some crying and others with puffy eyes. In one corner, a group of Italian runners watched the news with blank looks.
"I have no words," said Roberto Dell'Olmo, from Vercelli, Italy. Then later: "I would like that the money I give from the marathon goes to victims."
Gisela Clausen, of Munich, told her fellow runners about the cancellation as they walked in.
"You don't understand. We spend a year on this. We don't eat what we want. We don't drink what we want. And we're on the streets for hours. We live for this marathon, but we understand," she said.