A young and inexperienced Democratic candidate could win a congressional race in the Atlanta suburbs where Democrats hope to defy President Donald Trump by capturing a seat held by Republicans since 1979.

As results trickled in on Tuesday night, Jon Ossoff, 30, narrowly led a field of 18 candidates vying for a US House of Representatives seat that was vacated when Trump named Tom Price as his health secretary.

If Ossoff fails to win an outright majority of the vote in Georgia's 6th District, he will enter a June 20 runoff with one of the 11 Republicans in the race.

With 113 of 210 precincts counted, Ossoff, a documentary filmmaker and former congressional aide, held 50.3 percent of the vote.

Al Jazeera's Andy Gallacher, reporting from Sandy Springs, Atlanta, said Ossoff's chances of winning in a runoff would be slim with all the Republicans in the race uniting around the top candidate.

'A moral victory'

If that happens, the vote will still be a "moral victory" for the Democrats, given the district's history of robust support for the Republican Party, Gallacher said.

"Ossoff wasn't supposed to get anywhere near 50 percent," he added.

"If nothing else this race provides Democrats with hope for the 2018 midterm elections. His campaign has the kind of message and grassroots energy that could translate to other races and candidates across the country."

With the slogan "Make Trump Furious", Ossoff aimed to galvanise opposition to a president struggling with an approval rating that has not topped 50 percent since he took office on January 20, according to Reuters/Ipsos polling.

Ossoff has drawn volunteers and donors from out of state who see the race as a way to strike a blow against Trump. He raised a stunning $8.3m in the first three months of the year.

An Ossoff win would not tip the balance of power in Washington but could weaken the already shaky hold Trump has on his fellow Republicans by encouraging politicians to distance themselves from him.

The district, which encompasses a stretch of well-heeled suburbs north of Atlanta, has elected Republicans to the House since the late 1970s, but Trump carried it by only 1 percentage point in the November presidential election.

Republicans in the race are split among Trump supporters and candidates trying to hold the president at arm's length.

'Fresh face in Congress'

Greg Bluestein, a political reporter of the Atlanta Journal Constitution, said Ossoff's pledge to stand up to Trump resonates with voters.

"Voters here in the district also like his spirit, the fact that he's young and the fact that he would be a fresh face in Congress," he told Al Jazeera.

Trump criticised Ossoff on Twitter and said in a robocall that the Democrat would "raise your taxes, destroy your healthcare, and flood our country with illegal immigrants".

Democrat Jon Ossoff would be a disaster in Congress. VERY weak on crime and illegal immigration, bad for jobs and wants higher taxes. Say NO — Donald J. Trump (@realDonaldTrump) April 18, 2017

Ossoff said on CNN that Trump was misinformed about his positions and that he was focused on issues affecting the region, not Washington.

Republicans have responded with millions of dollars of spending of their own, casting Ossoff as an inexperienced outsider who does not live in the area he hopes to represent.

Ossoff, who grew up in the district, says he will move back if he wins.

The Republican Party avoided embarrassment last week when it narrowly held a conservative Kansas seat vacated when Trump tapped Republican Representative Mike Pompeo to head the Central Intelligence Agency.