Senator Bernie Sanders had "a fantastic night" on Tuesday, scoring an upset against former secretary of state Hillary Clinton in Michigan, the win defying all the polls done in the north-eastern industrial state since June last year.
The result surprised even Mr Sanders, who had to give an impromptu victory speech with just three campaign posters stuck on a wooden fence as a backdrop.
"This has been a fantastic night in Michigan," said the 74-year-old Vermont senator who received 49.9 per cent of the votes, pipping Mrs Clinton by less than two percentage points.
The win gave his campaign a huge boost as candidates move on to important states such as Ohio and Florida next week.
Professor John Clark, who is the chair of the political science department at Western Michigan University, called the Michigan primary an important one for Mr Sanders because "it is the first non-Southern state with a significant African-American population to hold its nominating contest so far this year".
"Senator Sanders did not get as many African-American votes in the South last Tuesday, so Michigan represents an opportunity for him to demonstrate his appeal to this important part of the Democratic coalition," Prof Clark said.
A CNN exit poll suggested that 65 per cent of black voters in Michigan supported Mrs Clinton, in contrast to 86 per cent in South Carolina.
"He (Mr Sanders) appealed more to young people and liberals and had a more aggressive outreach to African-Americans here than elsewhere," noted associate professor of political science Matt Grossmann from Michigan State University.
Mr Sanders' campaign manager Jeff Weaver told CNN that Tuesday's win was likely due to Mr Sanders' track record of opposing trade deals that had taken away jobs from the middle class in Michigan and that message "resonated across racial lines".
At their debate in Flint on Sunday, Mr Sanders portrayed Mrs Clinton as a champion of free trade, highlighting her support for the North American Free Trade Agreement and the Trans-Pacific Partnership.
Fifty-eight per cent of Michigan voters said in the CNN exit poll that trade with other countries took away United States jobs, and most of them chose Mr Sanders over Mrs Clinton.
But Prof Clark pointed out that while the result in Michigan would help Mr Sanders more than Mrs Clinton, both candidates boosted their delegate count.
After Tuesday's election, Mrs Clinton now has 1,221 delegates compared with 571 for Mr Sanders. A total of 2,383 delegates are needed for a candidate to clinch the Democratic nomination.
In Mississippi, Mrs Clinton won easily, as expected, with 82.6 per cent of the votes against Mr Sander's 16.5 per cent.
In her victory speech, she chose to direct her fire at the Republicans for the campaign they were running.
"The divisiveness and the mean- spiritedness, that's not going to move us forward. We need to stand united," she said.
Still, Mrs Clinton continues to battle the perception of being a dishonest politician as the presidential race continues.
In the Michigan exit poll, only 57 per cent of voters said she is honest and trustworthy, compared with 80 per cent for Mr Sanders.
In a statement after his win, Mr Sanders said: "The results here show that we are a national campaign. We already have won in the Midwest, New England and the Great Plains, and as more people get to know more about who we are and what our views are, we're going to do very well."