The Minnesota senator beat out former Vice President Joe Biden and a fellow senator, Elizabeth Warren of Massachusetts, but trailed Sen. Bernie Sanders, I-Vt., and Pete Buttigieg. Sanders won New Hampshire's primary by a margin of about 4,000 votes, or less than 2 percentage points, over the former mayor of South Bend, according to an NBC News projection.
Klobuchar introduced herself to the nation in a televised speech earlier in the evening.
"Hello America! I'm Amy Klobuchar and I will beat Donald Trump," she told a cheering crowd. "My heart is full tonight. While there are still ballots to count, we have beaten the odds every step of the way."
Voters 45 and older accounted for about two-thirds of Tuesday's voters, the NBC News Exit Poll found. Among those age 45 or older, Klobuchar had a slim lead over Buttigieg, 27 percent to 25 percent, according to the data. And among those who said the most recent debate was an important factor in their final decision, 30 percent chose Klobuchar.
The senator also did well with women: 67 percent of her voters were women, the most of any candidate, according to the exit poll data.
"Tonight in New Hampshire, as everyone had counted us out, even a week ago — thank you pundits — I came back and we delivered,” she told her crowd on Tuesday. "I never give up, but my story is nothing compared to the resilience that I have seen all over this country."
On caucus night, she turned Iowa's chaotic delay in reporting results to her advantage, giving a victory-tinged stump speech in primetime while the networks awaited word of what was going on. Amid outrage over the botched first contest, she renewed her pitch as a “steady hand in chaos."
And New Hampshire seemed keen on giving Klobuchar her shot: voters packed her events and into overflow rooms.
In Friday night's debate in Manchester, Klobuchar came out swinging, accusing Buttigieg of saying he’d rather watch cartoons than the impeachment trial.
"It's easy to go after Washington, because that's a popular thing to do," she said. "It's much harder to lead, much harder to take those difficult positions."
"There's no question, Amy Klobuchar is the one with the momentum here in New Hampshire," former New Hampshire Sen. John Sununu, a Republican, said on MSNBC Tuesday, touting the state’s open primary that allows voters of any party affiliation to cast a ballot. "And because of those undeclareds being part of the process, now a more mainstream centrist candidate like Amy Klobuchar can pull a lot of those votes on Election Day."
Another potential boost for the senator? An unusually large number of the state’s Democratic primary voters waited until the final days to settle on a candidate, too. According to the exit polls, half said they made up their minds in the last few days.
Now, Klobuchar's campaign turns its attention to Nevada, which will test candidates' support among Latino voters, a key Democratic constituency.
Her campaign told NBC News Tuesday night that it will have 50 campaign staffers on the ground in the state by the end of the week, and plans to spend at least $1 million on campaign ads in Nevada alone.
Jane C. Timm
Jane C. Timm is a political reporter for NBC News.