Sanders' lead slightly higher than a Public Policy Polling poll conducted in mid-August that found Sanders with 7% of the lead.
According to the NBC/Marist poll, even without Biden included, Sanders would still win the Granite State handily. In fact, he would lead Clinton by 11 points without Biden in the race.
The latest poll shows how Clinton's fortunes have sunk in the early-voting states, as Sanders has attracted record-setting crowds and built momentum with his populist, anti-establishment message.
In July, Clinton and Sanders' positions were essentially reversed, with the former secretary of state taking home 42% to Sanders' 32%.
See photos of Bernie Sanders on the campaign trail:
Bernie Sanders through the years
Bernie Sanders now has a commanding lead over Hillary Clinton in a key primary state
Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, speaks during an event in Iowa Falls, Iowa, U.S., on Monday, Jan. 25, 2016. With a week to go until the Iowa caucuses and the Democratic presidential race there in a virtual dead heat, Hillary Clinton and Sanders are mapping out divergent paths toward winning the first votes of the nomination process. Photographer: T.J. Kirkpatrick/Bloomberg via Getty Images
Washington, UNITED STATES: Newly-elected senators meet with Senate Minority Leader Harry Reid (R), D-NV, in Washington, DC 13 November 2006. From left are: Senator-elect James Webb, D-VA, Senator-elect Bernie Sanders, I-VT, Senator-elect Amy Klobuchar, D-MN, and Reid. AFP PHOTO/Karen BLEIER (Photo credit should read KAREN BLEIER/AFP/Getty Images)
US Congressman Elliot Engel (L) takes pictures next to US Senator Bernie Sanders after being dressed as Bouale leaders by public notaries of the Kouadioyaokro village, 150 km from Abidjan, 09 November 2008. US Senators Tom Harkin and Bernie Sanders visit comes ahead of a July 2008 certification deadline to ensure cocoa heading to the United States -- the third largest importer of Ivorian cocoa -- has not been produced with child labour. AFP PHOTO/ISSOUF SANOGO (Photo credit should read ISSOUF SANOGO/AFP/Getty Images)
COLUMBIA, SC - APRIL 25: Potential Democratic presidential candidate Sen. Bernie Sanders (R) (I-VT) delivers remarks at the South Carolina Democratic Party state convention April 25, 2015 in Columbia, South Carolina. Sanders joined former Maryland Gov. Martin O'Malley and former Sen. Lincoln Chafee in speaking to the convention. (Photo by Win McNamee/Getty Images)
WASHINGTON, DC - APRIL 20: U.S. Sen. Bernie Sanders (I-VT) participates in a 'Don't Trade Our Future' march organized by the group Campaign for America's Future April 20, 2015 in Washington, DC. The event was part of the Populism 2015 Conference which is conducting their conference with the theme 'Building a Movement for People and the Planet.'
(Photo by Win McNamee/Getty Images)
U.S. Senator Bernie Sanders, an Independent from Vermont and 2016 U.S. presidential candidate, greets supporters during a campaign rally in Madison, Wisconsin, U.S., on Wednesday, July 1, 2015. Sanders said he had attracted 200,000 donors as of mid-June and his campaign had raised $8.3 million online through June 17, according to FEC filings by ActBlue, the fundraising platform that he and some other left-leaning candidates and causes use. Photographer: Christopher Dilts/Bloomberg via Getty Images
PORTLAND, ME - JULY 6: Vermont Sen. Bernie Sanders speaks at the Cross Insurance Arena while campaigning in the Democratic presidential primary. (Photo by Derek Davis/Portland Press Herald via Getty Images)
Supporters hold up signs at a campaign rally for Senator Bernie Sanders, an Independent from Vermont and 2016 U.S. presidential candidate, in Madison, Wisconsin, U.S., on Wednesday, July 1, 2015. Sanders said he had attracted 200,000 donors as of mid-June and his campaign had raised $8.3 million online through June 17, according to FEC filings by ActBlue, the fundraising platform that he and some other left-leaning candidates and causes use. Photographer: Christopher Dilts/Bloomberg via Getty Images
PORTLAND, ME - JULY 6: Vermont Sen. Bernie Sanders speaks at the Cross Insurance Arena while campaigning in the Democratic presidential primary. Sen. Bernie Sanders greets supporters after speaking in Portland. (Photo by Derek Davis/Portland Press Herald via Getty Images)
PHOENIX, AZ - JULY 18: U.S. Sen. Bernie Sanders (I-VT) speaks to the crowd at the Phoenix Convention Center July 18, 2015 in Phoenix, Arizona. The Democratic presidential candidate spoke on his central issues of income inequality, job creation, controlling climate change, quality affordable education and getting big money out of politics, to more than 11,000 people attending. (Photo by Charlie Leight/Getty Images)
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Clinton has also seen her support erode in Iowa, where she's dropped to 37% support from 50% support in June, according to a Bloomberg Politics/Des Moines Register poll out last week. In NBC/Marist's Iowa survey, she leads by 11 points in Iowa, compared with a 29-point lead in July.
"It looks like what people call the era of inevitability is over," Iowa pollster J. Ann Selzer said in a Bloomberg Politics/Des Moines Register press release. "[Clinton] has lost a third of the support that she had in May, so anytime you lose that much that quickly it's a wake-up call."
But despite Sanders' momentum in early states, pollsters and analysts caution about his staying power deep into the primary.
The senator is still drawing the majority of his support from a pool of mostly white, more liberal voters. Pollsters have predicted for some time that Sanders' strength among this demographic could help him perform well — and even win — in Iowa and New Hampshire, which are both dominated by white Democratic voters.
The same is not true in other primary states, where the coalition of Democratic primary voters is far more diverse. This is seen as a boon to Clinton, whose support among African-American voters in Democratic polls is consistently hovering around 70-80%.
"If Sanders wins Iowa or New Hampshire, it will build a lot of momentum for him that will help in the states that follow, but he's still going to struggle in places like South Carolina with large black populations and Nevada with large Hispanic populations unless he improves his appeal to nonwhite voters," Tom Jensen, the director of PPP, told Business Insider in July.
And Clinton is still seen favorably by the majority of Democratic voters.
Sunday's NBC/Marist poll found her that 69% of New Hampshire Democrats view her favorably, down just 2% from the same poll in July. And 67% of Hawkeye State Democrats see her in a favorable light, which is down 7 points from July. More Democratic voters have a favorable impression of Biden in both states, however, while Sanders has higher net-favorable scores.