AFP

BOSTON MITT Romney edged out rival Rick Santorum in a nailbiter vote in Ohio as he tightened his grip on the 2012 Republican presidential nomination with a string of Super Tuesday wins.

Santorum kept his hopes alive with a trio of victories in North Dakota, Oklahoma and Tennessee, but Romney took six states: Idaho, Massachusetts, Virginia, Vermont, Alaska and — in the most closely watched contest — Ohio.

Former House speaker Newt Gingrich won resoundingly in his home state of Georgia, giving him an outside chance of rebooting his bid if he can gain some momentum in a clutch of upcoming battles in the conservative Deep South.

But it was the Rust Belt state of Ohio, which is expected to be a key battleground when President Barack Obama takes on the Republican nominee in the November 6 general election, that was the story of the night.

Romney ended up taking the state by more than 10,000 votes, or one percent of the vote, denying Santorum his central argument that he alone can compete against Obama in working- class, Midwestern swing states.

“We’re on our way,” Romney told supporters in a ballroom in the Westin Hotel in Boston, with his wife Ann beaming proudly at his side.

“I’m not going to let you down. I’m going to get this nomination.” At a “victory” party in Steubenville, Ohio, Santorum loyalists cheered after he won Oklahoma, but the late Ohio loss was to leave a sour taste in their mouths.

Santorum, 53, a devout Roman Catholic who fiercely opposes abortion and gay marriage, has billed himself as the only authentic conservative in the race who understands working-class voters and can beat Obama in the fall. “We have won in the West, the Midwest and the South and we’re ready to win across this country,” he told an ear-splitting rally.

But Santorum’s radical views have alienated some moderates, and after the Ohio setback serious questions will be asked about his electability. Romney, 64, won a majority of the 10 states in play, but lingering doubts remain as he has struggled to win in the South, with Santorum and Gingrich sweeping Georgia, Tennessee and Oklahoma.