"Now the hold is off, and I am open for business, 100 percent of the time and really looking forward to working with you on behalf of this city and state that we love," Clinton told the group.
Mayor Michael Bloomberg hosted the fete on his own dime, but the billionaire said earlier in the day he has no plans to help with Clinton's multimillion-dollar campaign debt.
The event, at which guests sipped Big Apple martinis and dined on barbecue, was not a fundraiser, although some of Clinton's top fundraisers were in attendance, along with Gov. David Paterson, Sen. Charles Schumer and former Mayors Ed Koch and David Dinkins.
Organizers said more than 400 guests attended the celebration, which was held at the official mayoral residence, Gracie Mansion; Bloomberg lives at his own town house and uses the official mansion for ceremonial events.
The menu included hot dogs, burgers and chicken on the grill, with mini cupcakes and ice cream sundae stations.
Bloomberg called Clinton a "great ambassador for New York."
"History will record her as a giant in her own right who carried forward the legacy of great New York leaders," he said.
Bloomberg did not host a party for his Republican predecessor, Rudolph Giuliani, another New Yorker who ran for president this year.
Bloomberg and Clinton have a complicated history: While they always exchange warm words publicly, Bloomberg never quite got over the fact that Clinton did not cross party lines and endorse him for re-election in 2005, when he was still a Republican and was running against a Democrat whose mayoral bid was a long shot.
And he did not endorse her or anyone else in the primary. Thus far he has not said whom he'll support in the general election.
For much of the Democratic presidential primary race, Bloomberg also was considering mounting his own independent presidential bid, but eventually he decided to stay out of the race. During those months, he expressed measured praise for Clinton, calling her a good senator who has been there whenever he needed her.
Clinton has been more reserved about Bloomberg over the years. She occasionally commends him for advocating the city's interests in the causes they share, such as fighting for homeland security money and aid for sick ground zero workers.
During her brief remarks at the party, Clinton teased Bloomberg for his fascination with running for the White House, joking that he and his political adviser Kevin Sheekey seemed so curious about the workings of her campaign once it was over - an interest she mistook as concern from friends.
"He was so interested in me ... I've always liked him, but, my gosh, I felt so special," she cracked. "And I noticed all through the conversation he was taking notes and Kevin was recording it, so I know that somewhere all this information will be put to good use."