Romney has for weeks has been expected to win in the Granite State's primaries. He has held double-digit leads in every New Hampshire poll since April, except one, and is ahead of his rivals by a wide margin.
But the real contest is for the No. 2 spot. Jon Huntsman has picked up steam in recent days and edged closer to Rep. Ron Paul, who has been polling in second place. For the former Utah governor, who has failed to qualify for the primary ballot in three states, this could be a make-or-break event.
Preliminary exit polls showed that concerns about electability, economic discontent and a less conservative but more divided base than in Iowa last week were helping to shape the New Hampshire primary today. Voters appeared to be looking for a candidate best suited to defeat President Obama, with independents coming to the polls in what could be record numbers.
The small village of Dixville Notch, population nine, kicked off the nation's first primaries this morning. Two of the town's residents voted for Romney and two went in favor of Huntsman, the former Utah governor who has put all his campaign efforts into the Granite state.
Romney edged out his competitors, however, as more voters turned to the polls. In Hart's Location, the second precinct to report its results, the former governor of neighboring Massachusetts received five votes, one more than Paul.
Romney, who owns a vacation home in New Hampshire, is the clear front-runner in a primary that is expected to drive a record number of voters to the polls. Twelve delegates are up for grabs in today's race.
New Hampshire Secretary of State Bill Gardner estimates that 250,000 ballots will be cast in today's Republican race, breaking the previous record of nearly 240,000 votes in 2008.
A scrum of supporters and reporters surrounded candidates as they worked the polling sites in the state's largest city. At the Webster school, Romney and Newt Gingrich were engulfed by a storm of cameras as two reporters were pushed to the ground in the media circus. Security kept the press behind barricades to allow voters to enter the polling station.
Rick Santorum was also scheduled to attend but staffers said they changed plans when they saw "the mob." Romney's security team quickly whisked the former governor away after he briefly intermingled with the crowd.
Today's primary is especially important for Huntsman. His "Our Destiny" political action committee has spent the most money on advertisement in New Hampshire, hoping to draw in more moderate conservatives and the independent voters who make up a significant chunk of the electorate and can vote in the primaries.
In recent days, President Obama's former ambassador to China has attempted to put a positive spin on the main point of criticism against him: that he served under a Democratic president whom is now hoping to meet in a general election.
"He [Romney] is a person who wants to put politics first. For me it's country first," Huntsman said in a CNN interview this morning.
As for where his campaign goes after New Hampshire, Huntsman gave a rather cryptic answer: "If we can exceed the expectations set up by the pundit class, we're going to be just fine."
The real trouble for Romney, and one that has been exacerbated in New Hampshire, lies in his rivals' attacking his record at venture capital group Bain. Romney aggravated the situation Monday by giving them material that has been turned into a cellphone ringtone by Texas Gov. Rick Perry.
He told a crowd, "I like being able to fire people who provide services to me." Even though he was talking about how individuals can fire their insurance companies if they don't like them, the quote quickly became fodder for his competitors.
Huntsman played to Republican concerns about such quotes being dissected by Democrats if Romney is elected the GOP presidential candidate.
"Listen, if you're going to make statements like that, you become pretty much unelectable," Huntsman told reporters today. "Because if it isn't a Republican, it's going to be the Chicago campaign machine with a billion dollars at their sails that's going to take after comments like that."
Perry, who skipped New Hampshire after the debates this weekend and is campaigning in South Carolina, today likened companies such as Bain Capital -- without saying its name -- to "vultures" who sit on a tree limb, swoop down to eat the carcasses and leave the skeleton behind.
"Allowing these companies to come in and loot the, loot people's jobs, loot their pensions, loot their ability to take care of their families and I will suggest they're just vultures," Perry said at a town hall in Fort Mill, S.C. "They're vultures that sitting out there on the tree limb waiting for the company to get sick and then they swoop in, they eat the carcass. They leave with that and they leave the skeleton."
Perry's son Griffin, who often serves as a surrogate for his father on the road and has not been shy about voicing his opinions about other presidential candidates, jumped into the fray today with a tweet criticizing Romney.
"Mitt Romney knows how to lead," he wrote. "Lead people straight out the door with a pink slip."
But Romney found some sympathy among others, namely Paul who defended his rival's statement in an interview with ABC News' Jonathan Karl.
"I think they're wrong," Paul said of Romney's critics. "I think they're totally misunderstanding the way the market works. They are either just demagoguing or they don't have the vaguest idea how the market works."
Santorum told ABC News' Jake Tapper that Romney's comment sends the wrong message but he also cut his rival some slack.
"I am not too sure that is a very good message to a lot of folks out there," he said today. "It was certainly an inarticulate way of phrasing what he wanted to phrase, but it's a little bit of a gotcha."
Nevertheless, Romney's comment could pick up steam as candidates head to South Carolina on Wednesday, a state where the unemployment rate of nearly 10 percent stands above the national average.
"The Republican party in South Carolina is not based in big business," said Republican strategist and ABC News consultant Matthew Dowd. "It's working class. Blue collar. It's much more populist."
ABC News' Gary Langer, Elizabeth Hartfield, Emily Friedman, Arlette Saenz and Shushannah Walshe contributed to this report.