With nearly all of the votes counted, Romney had a lead of about one percentage point over Rick Santorum in the Ohio primary and was the apparent winner. Even with 100 percent of precincts reporting tonight, there still will be an estimated 40,000 votes outstanding.
For a candidate who was at one point expected to breeze through the Republican primary contests, the surprisingly close vote is almost a symbolic victory for Santorum, who continues to nag Romney at every turn despite being greatly outspent.
Exit polls found that more than half of voters in Ohio said Romney was the candidate most fit to beat President Obama. But when asked which candidate "best understands the problems of average Americans," fewer than one-quarter of voters picked Romney. About one-third chose Santorum in that category.
Ohio had been the most contested and watched vote for a week, after Romney's close primary win in Michigan, where he was born. Santorum led in the polls until just a few days ago, but on Tuesday, the race was as good as a tie.
The other primaries that Romney won were of no surprise — his home state of Massachusetts, where he was the governor; the neighboring New England state of Vermont; and battleground Virginia, where he was the only candidate on the ballot aside from Ron Paul. He also won the caucuses in Idaho.
Santorum triumphed in Tennessee, a southern state in which his conservative message has resonated, and in Oklahoma, the reddest state in the union. In both states, voters who called themselves religious and very conservative lifted Santorum over Romney, who has struggled for months to persuade the right wing of the party that he's right for them. He also won the caucuses in North Dakota.
"We have won in the West, the Midwest and the South, and we're ready to win across this country," Santorum told enthusiastic supporters in Ohio as the vote there was being counted.
The former Pennsylvania senator added, excitedly: "In every case, we overcame the odds. Here in Ohio, still too close to call."
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Santorum also pointedly needled Romney over his role in creating the Massachusetts health care program that was used as a model for the "ObamaCare" system hated by conservatives.
Romney, however, didn't mention Santorum in his speech, other than to congratulate him.
Speaking to his fans in Boston, Romney said that "I'm going to get this nomination," and he said his campaign has been focusing on tabulating the number of delegates he'll need to win it.
"We're counting the delegates for the convention, and it looks good," Romney said.
The bulk of Romney's speech was centered on denigrating Obama, mostly over his handling of the economy. He warned that "President Obama wants to raise your taxes," and suggested that Obama doesn't "tell the truth" or have "integrity."
And for the second time recently, perhaps underscoring his campaign's rapid spending of its war chest, Romney asked his supporters to "pledge your support at mittromney.com."
As expected, Newt Gingrich won the only Super Tuesday state to which he gave attention -- his home state of Georgia, which he represented as a member of Congress.
In a victory speech in Atlanta, Gingrich called himself the "tortoise" who will win the nomination and mocked the attention given to Santorum after the ex-senator won three primaries in states that the other candidates had mostly ignored.
"The news media, once again, desperate to prove Gingrich was wrong, suddenly said, 'Ah, now we have the person who's going to be the non-Romney,' " Gingrich said.
Making his pitch to his supporters, Gingrich called himself "the one candidate who can debate Barack Obama," drawing on one of his noteworthy strengths that has been evident in the nearly two dozen GOP primary debates.
As voters in 10 states made their picks for the Republican nomination tonight, Romney was working to write the final chapter of the primary season on the biggest single day of contests in the race.
Romney, wearing the crown of official front-runner after recent wins in Michigan, Arizona and Washington, has been battling for the nomination for longer than it once seemed he would be. His main rival, Santorum, emerged from nowhere first in Iowa and then in a string of states last month as the "conservative alternative" to Romney.
