Pete Buttigieg clung on to his narrow lead over Bernie Sanders after a new batch of votes in the Iowa caucuses were released, but the race still remained too close to call.
The former South Bend Mayor was ahead of the Vermont Senator by less than one percentage point with 92 per cent of precincts reporting by late on Wednesday night.
Elizabeth Warren was in third and former Vice President Joe Biden and Amy Klobuchar further behind in a race that has been marred by delays after the Iowa Democratic Party’s app for reporting results crashed.
The chaos surrounding the reporting breakdown has undermined the impact of the Iowa's election, which typically rewards winners with a surge of momentum heading into subsequent primary contests.
The two early leaders – Mr Buttigieg, the former mayor of South Bend, Indiana, and Vermont Senator Mr Sanders - are separated by 40 years in age and conflicting ideology.
Mr Sanders, a 78-year-old self-described democratic socialist, has been a progressive powerhouse for decades, and his rival, a 38-year-old former municipal official, represents the more moderate wing of the Democratic Party.
Mr Buttigieg is also the first openly gay candidate to earn presidential primary delegates.
President Donald Trump branded the Democrats' efforts to pick a candidate to challenge him at the 2020 US Presidential election "an unmitigated disaster".
Iowa is the US state that traditionally kicks off a presidential election campaign that culminates this year on November 3.
The Democrats' primary fight intensified in New Hampshire on Wednesday as Mr Biden took aim at both Iowa front-runners.
The former vice president suggested that Mr Sanders was unelectable and would hurt other Democrats on the ballot this fall should he represent the party in the general election.
He also charged that it would be "a risk" to nominate Mr Buttigieg because he hasn't been elected to a higher office than South Bend mayor.
Speaking at a candidate forum in New Hampshire, Buttigieg was focused on the issues. He said a shift in emotion from "guilt and doom" to pride is needed to propel the nation forward on climate change.
