Christopher J. Christie, campaigning as an agent of change, overwhelmed a powerful Democratic advantage Tuesday to defeat Gov. Corzine and become New Jersey's first Republican governor-elect in a dozen years.

Portrayed by Corzine as a referendum on President Obama's agenda, the campaign drew national scrutiny - and three visits from the president to support the incumbent.

But Christie fought aggressively, campaigning in cities and other Democratic strongholds. Christie, 47, a former U.S. attorney from the North Jersey town of Mendham, turned back both Corzine and a vigorous campaign from independent Chris Daggett.

The Associated Press declared Christie the winner shortly after 10 p.m.

Fifteen minutes earlier, Daggett had conceded at the Dolce Hotel in his hometown of Basking Ridge, not knowing who won but still worried about the state's future.

"Whether it's Jon Corzine or Chris Christie, they deserve the support of every one of us in New Jersey, because the problems of this state are significant," he said.

For the first time Tuesday, New Jersey voters chose a lieutenant governor, selecting Republican Monmouth County Sheriff Kim Guadagno. Running with Corzine was Democratic Bergen County State Sen. Loretta Weinberg.

And the rules on absentee or mail ballots changed this year, allowing voters to vote by mail without an excuse. Both campaigns persuaded voters to vote early. Early reports showed about 30,000 more mail ballots were cast in this race than the 91,000 cast in the 2005 governor's race.

Although New Jersey is a reliably blue state, the conditions could not have been better for a challenger to unseat Corzine, an unpopular incumbent running in a recession. Unemployment went up to 9.8 percent - a rate higher than in nearby Pennsylvania and New York state. State revenues fell, and Corzine raised taxes on the wealthy and cut back property-tax rebates for many in the middle and upper classes.

Christie rigidly stuck to a plan of not giving voters too many specifics about his agenda, fearing the Corzine money machine would turn them against him. That stymied some voters ready for change but looking for a reason to choose Christie.

"A good proportion of voters were expecting Christie to come out and be hard-hitting about what he would do about the budget and property taxes," said Brigid Harrison, a Montclair University political scientist. That didn't happen.

Daggett, 59, a former moderate Republican, did well in debates and came close to convincing voters that he could win, but crumbled in the final two weeks of the race.

Democrats spent Tuesday getting urban voters to the polls, trying to exploit their numerical advantage over Republicans.

County Democratic machines were supplemented by about 15,000 union members, angered by Christie's promises to extract concessions from state workers, the threat to teachers' unions that he would open more charter schools and give out school vouchers in failing districts, and his opposition to using only union workers on public-works projects.

The GOP pushed hard in suburban Morris, Ocean, Burlington, Bergen and Monmouth Counties, as well as towns rimming the cities, where they hoped they could find Reagan Democrats - or their adult children - to vote for Christie.

For the technology-minded, Corzine's campaign texted voters throughout the day. Republicans asked supporters to list their Facebook status as "Voting for Chris Christie."

And Daggett sent out e-mails reminding voters to spend a little extra time to find his name on the ballot. In only two of the state's 21 counties did Daggett's name appear near the names Christie and Corzine.

At the polls, voters reflected on their choices.

Lisa Watson, 36, of Deptford, said she had briefly considered voting for Daggett but changed her mind at the last minute.

"I was worried that a vote for Daggett was really a vote for Christie against Corzine," Watson said. "I absolutely do not want to see Christie as governor of New Jersey."

Dog groomer Susan Finn, 53, of Washington Township, stuck to her guns.

She voted for Daggett because "the other two threw mud and never said what they would do," she said, adding that she admired Daggett for saying, "If you don't have the money, you don't spend it."

Frank Pino, 56, a union electrician from Deptford, said that while his union had urged him to vote for Corzine, in his heart he wanted to vote for the Republican. "I'm mad at Corzine, but in the end I voted for him," Pino said.

In Ocean County's Tuckerton, Frank Kremer, 47, said: "I cannot see how anyone, Democrat or Republican, would ever vote for Jon Corzine again. Even if I thought he did do a good job, I wouldn't have voted for him because I'm a Republican."

The content and the crush of television advertising helped shape the race, one of only two gubernatorial contests. In Virginia, former state Attorney General Robert F. McDonnell, a Republican, defeated Democrat R. Creigh Deeds, a state senator.

Corzine, 62, a Wall Street millionaire, relentlessly attacked Christie in the summer and early fall on ethics issues and even on his girth, a move that might have cost Corzine some points. He wanted to marginalize Christie's background as a successful U.S. attorney, whose central argument in this campaign was that he had the executive experience to lead a troubled state.

Corzine outspent Christie in September and early October on television ads by almost 3-1, costing Christie his substantial lead. In the end, Corzine may have spent $30 million, much of it his own money, on the race.

Christie came back on television in force by mid-October but was able only to keep the race at a dead heat in polls. He had another problem by then: Daggett. Christie and the Republican Governors Association spent time beating down Daggett, particularly with conservatives and Republican-leaning independents.

Christie must deal with a looming $8 billion deficit and would have the chance to appoint four of the seven members of the state Supreme Court.

Contact staff writer Cynthia Burton at 856-779-3858 or cburton@phillynews.com.

Contributing to this article were staff writers Rita Giordano, Jan Hefler, Adrienne Lu, Maya Rao, Matthew Spolar, and Jacqueline L. Urgo.