Super Tuesday has been the night that settles the Republican presidential nomination in recent campaigns.
With voters in ten states casting ballots, Mitt Romney’s supporters hoped their man would see off his nearest rival Rick Santorum.
But he only managed a narrow win in the blue collar swing state of Ohio.
Romney came top in five other states, while Santorum picked up three victories.
He finished first in Tennesse, Oklahoma and North Dakota.
The former Pennsylvania senator has painted himself as the only true conservative in the race, taking a strong stance on social issues.
Newt Gingrich, the former speaker of the House of Representatives, won his home state of Georgia.
He has refused to suspend his campaign and even predicted that he would make a third comeback in later primary contests.
Texas Congressman Ron Paul is still without a state victory, but his camp believes he can still secure the nomination.
There are more six more contests to be held within the next week, with staunchly conservative states Kansas, Alabama and Mississippi having their say.