Updated at 7:44 a.m. ET — Mitt Romney scored a narrow victory over Rick Santorum in the Ohio presidential primary following a hard-fought campaign that had been perceived as a turning point in the battle for the Republican presidential nomination. NBC News projected he was the apparent winner in that state.

Both Romney and Santorum won several Super Tuesday caucuses and primaries, but none more prized than Romney's victory in Ohio. The former Massachusetts governor was able to ride a wave of momentum out of Michigan, where he also closely battled Santorum, to erase the former Pennsylvania senator's lead in Ohio over the past week.

The trajectory of the Republican campaign hinged in large part on Ohio, and now Romney may claim the imprimatur associated with winning a state that's considered an essential step toward victory in the general election.

But a margin of just a few thousand votes separated Romney and Santorum, representing a kind of moral victory for Santorum given the way the Romney campaign and a supportive super PAC heavily outspent him in Ohio.

In all, Romney appeared to have sealed victories in six Super Tuesday states. In addition to Ohio, NBC News projected Romney as the winner in Vermont, Massachusetts, Idaho and Virginia (where only he and Texas Rep. Ron Paul appeared on the ballot). Early Wednesday, Romney added Alaska to his tally.

NBC News projections suggested that Santorum won Tennessee, Oklahoma and North Dakota, while former House Speaker Newt Gingrich won Georgia, the state from which he had served as a representative in Congress.

But neither Santorum nor Gingrich, buoyed by their own wins, seemed any closer by the end of the night to ending their campaigns, reflecting the lingering doubts over Romney among conservatives, which were underscored in exit polling.

Check out the full Super Tuesday results here

"We're going to win a few, we're going to lose a few. But as it looks right now, we're going to get at least a couple gold medals and a whole passel full of silver medals," Santorum said in Steubenville, Ohio, before the state's results were announced. "We have won in the West and the Midwest and the South, and we're ready to win across this country."

The states with contests Tuesday were Georgia, Virginia, Vermont, North Dakota, Ohio, Massachusetts, Oklahoma, Tennessee, Idaho, Alaska and Wyoming.

Slideshow: Voters head to polls on Super Tuesday

Mark Humphrey / AP

See pictures from around America as 11 states hold contests that will award a combined 424 delegates in the Republican primary.

Launch slideshow

More delegates were up for grabs on this Super Tuesday than had been previously allocated to the remaining GOP candidates after two months of voting, according to NBC News projections. Between the 10 states holding primaries or caucuses and Wyoming, which will allocate five of its 26 delegates, a total of 424 of the 1,144 delegates needed to win the nomination are at stake.

Delegate race tells a different GOP story

In addition to Ohio, NBC News projected Romney as the winner in Vermont, Massachusetts, Idaho and Virginia (where only he and Texas Rep. Ron Paul appeared on the ballot). Early Wednesday, Romney added Alaska to his tally.

"There are three states under our belt, and counting. We're going to get more by the time this night is over," Romney told supporters in Boston before firmly declaring: "I'm going to get this nomination."

'We're doing some counting'
Romney emerged as the night's winner in terms of delegate haul, a point which he emphasized in his speech.

"Tonight we're doing some counting," he said. "We're counting the delegates for the convention and that looks good, and we're counting down the days to the convention, and that looks better."

But exit polls showed Romney continued to struggle with the most conservative voters, the core of the Republican Party, in states like Ohio and Tennessee -- arguably the two most competitive contests held Tuesday.

But Romney performed well among voters who consider the economy their top issue, or who rated a candidate's ability to beat President Barack Obama in November -- two key selling points in the former Massachusetts governor's campaign.

Some Republicans had hoped that Super Tuesday would help propel the Republican race into a new stage, one that draws toward a conclusion given the growing negative cloud surrounding the GOP race.

Santorum camp asking conservatives to pressure Gingrich to drop out

Forty percent of respondents, for instance, said in Monday's NBC News/Wall Street Journal poll that the primary process has given them a less favorable opinion of the Republican Party. And more independent voters said in a separate Washington Post/Pew Research Center poll that their impression of the GOP candidates was getting worse as a result of the primary than those who said their opinion was improving.

Gingrich decried that negativity in his election night speech, one in which he vowed to press forward. 

"I want you to know that, in the morning, we are going on to Alabama. We're going on to Mississippi. We're going on to Kansas," he said to cheers. "And that's just this week."

A strong performance by Romney might have moved more Republicans who had harbored doubts about the ex-governor off the fence, and finally create some sustained momentum for Romney. Still, momentum in the primary has come in fits and starts, threatening to make the Republican campaign into a prolonged battle over delegates.

Santorum expressed optimism as he addressed supporters at a rally in Ohio, saying that he and his family are "making a sacrifice for a very big goal," replacing Obama in the White House.

"They are decimating each other ... independent voters are fleeing him," Obama campaign adviser David Axelrod said Tuesday night on NBC in regard to Romney and the GOP campaign. "I feel good about how things have evolved in the last six months."

While the day boasted more primaries and caucuses than any other in 2012, it was a shadow of Super Tuesday in 2008, when there were 20 Republican contests.

There was another big difference, a trend away from winner-take-all contests to a system of allocating delegates in rough proportion to a candidate's share of the popular vote.

Sen. John McCain won eight states on Super Tuesday in 2008 and lost 12 to Romney and Mike Huckabee combined. But six of McCain's victories were winner-take-all primaries, allowing him to build an insurmountable delegate lead that all but sealed his nomination

The Associated Press contributed to this report.