Mitt Romney secured a close victory in Ohio but failed to land a knockout blow against rival Rick Santorum on "Super Tuesday," raising the odds of a drawn-out battle for the Republican presidential nomination between the party's establishment and its grassroots conservatives.

Romney won five of the 10 state contests on  Tuesday but his margin of victory was uncomfortably slim in Ohio, the night's biggest prize. Ohio is a politically divided state sure to be hotly contested in the November 6 election between the eventual Republican nominee and Democratic President Barack Obama.

Romney moved closer to the 1,144 delegates needed to win the party's nomination, but a strong showing by Santorum underscored the front-runner's continued inability to win over large swathes of the Republican base, who view his past as a moderate Massachusetts governor with suspicion.

"We're counting up the delegates for the convention and it looks good," Romney told supporters in his home state of Massachusetts.

Romney won easily in Massachusetts, as well as liberal-leaning Vermont and in Idaho, where his fellow Mormons make up a substantial slice of the electorate. Romney also won Virginia, where Santorum failed to qualify for the ballot.      Santorum said his victories in Tennessee, Oklahoma and North Dakota proved he was the best candidate to represent the party's conservative philosophy.

Newt Gingrich won his home state of Georgia and said he would stay in the race. With most of the votes counted in Ohio, Romney led Santorum by 38 percent to 37 percent and TV networks projected he would take the state. Romney ran strongest in and around the state's largest cities, while Santorum carried the rural areas.

Exit polls showed that Ohio voters viewed Romney as more likely to defeat Obama, but thought Santorum was more sympathetic to average Americans' concerns.

Romney, who built a fortune of at least $200 million as a private-equity executive, has struggled to connect with conservatives and blue-collar voters. A convincing win in Ohio would have put many of those doubts to rest.     
Romney extended his lead among delegates, not least because Santorum's thinly staffed campaign failed to qualify for delegates in several parts of Ohio. Under new rules designed to lengthen the nominating battle, most states at this stage of the process award delegates on a proportional basis.

Santorum, a former US senator from Pennsylvania, has won support of religious conservatives thanks to his opposition to gay marriage and his views on other hot-button social issues. He also has targeted blue-collar voters, but his controversial comments about birth control and the role of religion have alienated moderate-leaning voters, especially younger women who will be a key constituency in November. - Reuters