CONCORD, N.H. — Sen. Hillary Rodham Clinton powered to victory in New Hampshire's Democratic primary Tuesday night in a startling upset, defeating Sen. Barack Obama and resurrecting her bid for the White House. Sen. John McCain defeated his Republican rivals to move back into contention for the GOP nomination.

"I felt like we all spoke from our hearts, and I am so gratified that you responded," Clinton said in victory remarks before cheering supporters. "Now together, let's give America the kind of comeback that New Hampshire has just given me."

Her victory, after Obama won last week's Iowa caucuses, raised the possibility of a prolonged battle for the party nomination between the most viable black candidate in history and the former first lady, seeking to become the first woman to occupy the Oval Office.

"I am still fired up and ready to go," a defeated Obama told his own backers, repeating the line that forms a part of virtually every campaign appearance he makes.

McCain's triumph scrambled the Republican race as well.

"We showed this country what a real comeback looks like," the Arizona senator told The Associated Press in an interview as he savored his triumph. "We're going to move on to Michigan and South Carolina and win the nomination."

Later, he told cheering supporters that together, "we have taken a step but only a first step toward repairing the broken politics of the past and restoring the trust of the American people in their government."

McCain rode a wave of support from independent voters to defeat former Gov. Mitt Romney of Massachusetts, a showing that reprised the senator's victory in the traditional first-in-the-nation primary in 2000.

It was a bitter blow for Romney, who spent millions of dollars of his own money in hopes of winning the kickoff Iowa caucuses and the first primary — and finished second in both. Even so, the businessman-turned politician said he would meet McCain next week in Michigan primary, and he cast himself as just what the country needed to fix Washington. "I don't care who gets the credit, Republican or Democrat. I've got no scores to settle," he told supporters.

After Iowa, Clinton and her aides seemed resigned to a second straight setback. But polling place interviews showed that female voters — who deserted her last week — returned to her column in New Hampshire.

She also was winning handily among registered Democrats. Obama led her by an even larger margin among independents, but he suffered from a falloff in turnout among young voters compared with Iowa.