Mitt Romney has emerged as the biggest winner on the busiest day yet in the race to secure the US Republican presidential nomination, but the battle to challenge Barack Obama in November looks set to rumble on.
The closest contest was in Ohio, where frontrunning Romney won 38 per cent of the vote, edging out main challenger Rick Santorum by a margin of about 12,000 ballots.
On a day dubbed "Super Tuesday", Romney also picked up victories in Massachusetts, Virginia, Vermont, Idaho and Alaska, while Santorum won in Tennessee, Oklahoma and North Dakota. Newt Gingrich, in third place in the race, won his home state of Georgia.
With 419 of the 1,144 delegates needed for the nomination up for grabs, Tuesday could have been a moment for Romney to cement himself as the party's strongest candidate. But Santorum's wins and the neck-and-neck race in Ohio, considered a national bellwether, meant he failed to deliver a knockout punch.
But Romney looked toward the general election against Obama in his victory speech.
Addressing supporters in Boston, Romney said: "This president's run out of ideas. He's run out of excuses, and in 2012, we're going to get him out of the White House. This campaign is not about a name on the ballot. It's about saving the soul of America."
Al Jazeera's John Hendren, reporting from Columbus, Ohio, said the day had been a "mixed bag" for Romney.
"But if there's one headline coming out of this it is that Mitt Romney won Ohio - and Ohio was the crown jewel," Hendren said.
Ohio allocates 48 of its 63 delegates based on the winner in individual legislative districts, meaning Romney's overall win did not deliver him an overwhelming haul of delegates. But the state is deemed an especially important prize because it has voted for the winner in presidential elections since 1964, when it favoured Lyndon Johnson over Barry Goldwater.
"We're going to get at least a couple of gold medals and a whole passel full of silver medals," Santorum told supporters in Ohio. "We've won in the West, the Midwest, in the South and we're going to win across this country."
Gingrich, speaking in his home state of Georgia, said he would continue in the race.
"In the morning, we are going on to Alabama, we are going on to Mississippi, we are going on to Kansas, and that is just this week," he told supporters at his Atlanta headquarters.
Ron Paul, a congressman from Texas campaigning on a libertarian platform, is also running for the candidacy.
A strong showing on Super Tuesday is considered crucial to a bid for the White House by showing that a candidate can compete across states with diverse demographics and political leanings.
Four years ago, the day proved decisive in the race for the nomination, with Romney conceding defeat to eventual Republican candidate John McCain.
Palin: Anything is possible
Although Romney failed to score the sort of knockout punch that could have sewn up the nomination in his favour, Al Jazeera's Alan Fisher, reporting from Boston, said his latest win was a significant boost for his campaign.
"That is a big win for him and, mathematically, it is now becoming almost impossible for anyone to catch Romney to reach that magic number of 1,144 - the number of delegates you need for the national convention in Tampa [Florida] in August," said our correspondent.
With the back-and-forth competition still undecided, some are starting to speculate about a possible compromise convention when the Republican Party gathers to select their candidate later this year.
If no one is able to win the 1,144 delegates needed, then the floor could open to potential candidates not currently in the race.
They could include Sarah Palin, who was Republican vice-presidential nominee in 2008 and Jeb Bush, former governor of Florida and younger brother of ex-president George Bush.
Palin has declined to rule out throwing her hat in the ring if pressed to run for the nomination.
Speaking as she voted in the caucuses in her far northwestern home state, the former vice-presidential nominee also said she might consider running for the White House in 2016.
"Anything is possible for an American. And I don't discount any idea or plan that at this point isn't in my control - anything's possible."
"I would seriously consider whatever I can do to help our country, to put things back on the right track," she said in her hometown of Wasilla, Alaska.