Mitt Romney emerged as the biggest winner on the busiest day yet in the race to secure the US Republican nomination with victories in the key swing state of Ohio and five other states, but the battle to challenge Barack Obama in November looked set to rumble on.In the closest contest of the night, Romney, the longtime frontrunner in the race, eventually edged out main challenger Rick Santorum, by 38 per cent to 37 per cent - or about 12,000 votes - with 96 per cent of ballots counted.   On the 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 won his home state of Georgia.Alaska also held caucuses on a day that saw 419 delegates up for grabs of the 1,144 delegates needed to win the nomination.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: "It was a bit of a mixed bag for Super Tuesday, but if there’s one headline coming out of this it is that Mitt Romney won Ohio - and Ohio was the crown jewel.”Although Ohio divides its 63 delegates proportionally, the state is deemed an especially important prize because it has voted for the winner in presidential elections since 1960, when it favoured Richard Nixon over John F Kennedy.