On the biggest single day in the rollercoaster ride that is the Republican presidential race, Romney won 38 per cent of the vote in Ohio in early, unofficial results, while Santorum was right behind him at 37 per cent.
Romney crushed the competition in Massachusetts, where he served as governor for four years, and also handily won Virginia, Vermont, Idaho and Alaska.
Santorum, meantime, won in Tennessee and Oklahoma, where his stances on hot-button social issues play well with those states' Christian evangelical voters, and in North Dakota, a state in the midst of an oil boom.
But it wasn't a terribly super Tuesday for Romney thanks to the death match for the biggest political prize of the night — blue-collar Ohio, a crucial swing state in presidential elections.
Santorum bested Romney in early results for most of the night, but the Mormon millionaire finally pulled away in the state's urban areas, eking out a win on a day he'd hoped would catapult him out of reach of his opponents.
Instead, his candidacy remains plagued by fears that he can't decisively win crucial states or unite the party's base, itself bitterly divided among social conservatives, Christian evangelicals, anti-spending Tea Party activists and moderate, pro-business Republicans.
He acknowledged that the path to Super Tuesday hadn't been easy in a speech in Boston after winning the Massachusetts primary.
"It's been a long road getting to Super Tuesday, I've got to be honest," he said.
"I'm not going to let you down; I'm going to get this nomination. We're going to take your vote, this huge vote in Massachusetts, and take that victory all the way to the White House."
Santorum was delighted with his three-state victory.
"We have won in the West, the Midwest and the South and we're ready to win across this country," Santorum said, pointing out that Romney vastly overspent him in every jurisdiction. "In every case, we overcame the odds."
Romney was looking to clear a significant hurdle on Super Tuesday in his dash to secure the presidential nomination. Santorum, meantime, hoped some electoral triumphs would revive his flagging campaign and keep him nipping at the front-runner's heels.
Ohio was a key battleground.
The wealthy Romney trailed Santorum in the state for most of February, and they were neck-and-neck in the Rust Belt state heading into Super Tuesday. A loss in Ohio for either man would have represented a demoralizing and potentially damaging blow, taking the wind out of their sails as they headed into future contests in states that include Alabama, Mississippi and Kansas.
Gingrich, who served Georgia as a U.S. congressman for two decades, easily took the state with about 45 per cent of the vote.
The former speaker of the House of Representatives, however, sputtered in other states. Nonetheless, Gingrich suggested the Georgia win portended future victories in a tweet that spoke of impending "March momentum."
"This is amazing," he said in Georgia in a typical Gingrich victory speech, snidely chastising "the elite" of the media, the punditry and the Republican party who have repeatedly written off his campaign.
"The national elites, especially Republicans, had decided a Gingrich candidacy was so frightening they had to kill it," he said, reiterating his belief that his debating skills would make him the best candidate to take on U.S. President Barack Obama in November.
Neither Santorum nor Gingrich were on the ballot in Virginia, limiting opportunities for both men to gain ground on Romney, who took about 58 per cent of the vote, according to early, unofficial results. Ron Paul won 43 per cent.
As Super Tuesday results poured in, former Alaska governor Sarah Palin — at a polling station in her state — made news by telling CNN she'd be willing to step into the race if no one's secured the nomination by the party convention in August.
"As I said, anything is possible and I don't close any doors that would be open out there," said Palin, the former vice-presidential candidate who has a contract with Fox News, in her most definitive response to the question.
"I wouldn't close that door."
With more than 400 delegates at stake in the 10 states, Super Tuesday represented a significant chunk of the 1,144 needed to secure the nomination.
Georgia, Ohio, Virginia, Tennessee, Oklahoma, Vermont, Massachusetts, Idaho, North Dakota and Alaska all held nominating contests.
Romney headed into Super Tuesday with momentum after eking out a victory over Santorum last week in Michigan, the state where the front-runner was born and raised. He also easily won Arizona's winner-takes-all contest, and was victorious in Saturday's caucuses in Washington state too.
Santorum's campaign surged in February after he won a trio of contests in the Midwest early in the month. He was looking to recapture that momentum on Super Tuesday.
On the campaign trail on Tuesday, Romney kept a disdainful focus on Obama, penning an editorial in the Washington Post that portrayed him as weak on foreign policy before assailing him again to the American Israel Public Affairs Committee.
"The president speaks of common interests. Let me be very clear about this: We do not have common interests with a terrorist regime," Romney said to applause.
"It is profoundly irrational to suggest that the ayatollahs think the way we do or share our values. They do not."
Santorum addressed the conference too, saying Iran has no reason to take the U.S. seriously when Obama talks of waiting for sanctions to work.
"From everything I've seen from the conduct of this administration, he has turned his back on the people of Israel," he said.
Republicans have been trying to woo Jewish voters, who cast their ballots overwhelmingly for Obama in 2008, by accusing him of being weak on Iran.
At a rare news conference at the White House later in the day, Obama fired back.
"Those folks don't have a lot of responsibilities," Obama said, adding their actual policies on what to do about Iran were strikingly similar to his own.
"If some of these folks think that it's time to launch a war they should say so, and they should explain to the American people exactly why they would do that and what the consequences would be. Everything else is just talk."Suggest a correction