Mitt Romney has won the Ohio Republican primary, one of six victories for the former Massachusetts governor on "Super Tuesday".
But his margin of victory in Ohio, at less than 1%, was narrow and Rick Santorum, the runner-up in Ohio, won in three other states and has significant momentum.
Overall Mr Romney won six of the ten states up for grabs last night, including Massachusetts, Vermont, Idaho and Alaska, where Ron Paul had hoped to secure his first win.
With most of the ten Super Tuesday states going to form, the concentration on Ohio became intense.
No Republican has become president without winning Ohio in an election, and no-one has spent more money than Mr Romney on trying to win the state.
When he spoke to his supporters, he put the most positive gloss on the situation, in an attempt to shift the emphasis to the fight against current Democratic President Barack Obama.
But Mr Romney failed to secure the knockout punch he had hoped for, virtually guaranteeing the race will continue for weeks or even months, with the candidates vowing to fight on to the Republican National Convention in August.
Mr Santorum is still in the race after winning Tennessee, North Dakota and Oklahoma and coming within a whisker of winning in Ohio.
His appeal to working class republicans and to religious conservatives is enduring.
With Mr Paul hardly showing and Newt Gingrich only winning his home state of Georgia, this seems to be a straightforward fight between Mr Romney and Mr Santorum.
In the race to get the requisite number of delegates, Mr Romney is winning but it is far from convincing.
Delegates are awarded by each state in the complex Republican Party nominating process, with one candidate needing to reach 1,144 delegates to declare victory.
More than 400 delegates were up for grabs on ''Super Tuesday'', nearly 40% of the total needed to secure the nomination.
