Final update at 12:15 a.m. 

Roughly five hours after polling locations closed, major networks began projecting that Georgia's 6th District special election would be heading toward a runoff on June 20.

That means Democrat Jon Ossoff and Republican Karen Handel, the race's top two vote-getters, will have nine more weeks of expensive and heating campaigning before voters will decide who will replace Tom Price, now Trump's health secretary, as the representative for Atlanta’s affluent, leafy northern suburbs in the House.

Ossoff, a 30-year-old documentary film maker and political novice, told his supporters late Tuesday that a runoff “shattered expectations.” "We will be ready to fight on and win in June if it is necessary," he said.

Earlier Tuesday evening, former Secretary of State Karen Handel vowed "start the campaign anew" on Wednesday, as her onetime Republican opponents began to coalesce around her. "Beating Ossoff and holding this seat is something that rises above any one person," she told supporters.

Outside groups poured millions into the nationally-watched contest, which was widely viewed as an early indicator of Trump’s popularity as he closed out his first 100 days in office. Even the president himself weighed in, via a series of attacks against Ossoff on Twitter, and he tweeted again moments after CNN called the race:

As of publishing time, with more than five-sixths of precincts reporting, Ossoff had won 48.6 percent of the vote in the 18-candidate field, and Handel 19.5 percent. Ossoff would have needed more than 50 percent of the vote to avoid a runoff.

Updated at 11:45 p.m. -- Data error slows Fulton returns

A rare malfunction could be the culprit behind a lengthy delay in counting Fulton County ballots, a development that's so far prevented Georgia election officials from calling the special election in the 6th congressional district.

Workers must now manually screen hundreds of ballots to ferret out the problem, according to our sister station WSB-TV:

The Fulton County news was quick to inspire some low-grade Twitter humor (there were plenty of Russia hacking quips), as well as a joking pledge from a Pennsylvania Democrat to introduce a bill in Congress that would send more money to Fulton County to hire more vote counters.

Meanwhile, secretary of state candidate Buzz Brockway used the opportunity to discuss his platform:

Updated at 11:20 p.m. -- Handel omits Trump 

If this 6th District race is considered to be first and foremost a referendum on Trump, then consider this:

Our colleague Michelle Baruchman later shared this readout from the Handel watch party:

But she never mentioned Donald Trump.

"Tomorrow, we start the campaign anew," she said. "Beating Ossoff and holding this seat is something that rises above any one person."

Updated at 11:00 p.m. -- Other candidates struggle to gain traction 

One thing that's fallen through the cracks of 6th District coverage so far is just how little traction candidates not named Handel or Ossoff were able to garner.

With two-thirds of precincts reporting, the bottom 13 candidates cumulatively netted only about 3 percent of the votes.

Being a Trump loyalist didn’t pay off. Bob Gray made allegiance to Donald Trump the cornerstone of his campaign, and he may have suffered for it. He got about 10 percent of the vote and came under a barrage of criticism over his pro-Trump bona fides. And Bruce LeVell, head of Trump’s diversity coalition, got less than 1 percent of the vote. He also put Trump at the center of his campaign, and even made a last-minute trek to the White House to visit with the president, who didn’t endorse any candidate in the race.

It wasn’t a good day for big-name Republican endorsers. Or for self-funders.

Judson Hill never gained much traction beyond a few Cobb precincts, and his endorsements from Florida Sen. Marco Rubio and former House Speaker Newt Gingrich didn’t get him very far. Dan Moody had an even worse night. The former state senator pumped more than $2 million into his own campaign, had the support of U.S. Sen. David Perdue and some of the most formidable operatives in the race. Yet he still hovered below double-digits.

The other four Democrats in the race barely mustered a few hundred votes between them, even as several vowed there would be no “coronation” for Ossoff. Ron Slotin, the only Democrat with elected experience, earned just a fraction of 1 point.

Updated at 10:18 p.m. -- Money, money, money 

Earlier Tuesday evening, Handel mentioned that Ossoff's lead is "what happens when you have $9 million, most of it from out of Georgia."

Let's take a quick look at that money, courtesy of the nonprofit Issue One, which advocates for campaign finance reform:

Ossoff indeed reported fundraising a staggering $8.3 million earlier this month, as we previously reported. Issue One estimates that nearly two-thirds of the money raised across all 18 candidates in the 6th District race went to Ossoff, and two-thirds of that dough was from small donors.

Separately, outside groups have poured just shy of $8 million into the race, roughly 60 percent of which from conservative groups attacking Ossoff, Issue One says. A third of all outside money spent in the race came from the Congressional Leadership Fund, a D.C. super PAC aligned with House Speaker Paul Ryan. Read their full report here.

Updated at 10:10 p.m. -- Runoff predicted 

Ossoff is still easily carrying the 6th District field, but his lead has narrowed, and some analysts are beginning to predict a runoff.

With half of precincts reporting, Ossoff has slightly more than 50 percent of the vote. Handel is at 18 percent.

The major networks have yet to call the race,  but many Republicans whose knuckles were turning white earlier Tuesday night are beginning to show some signs of confidence:

Updated at 9:05 p.m. -- Watch party dispatches 

Ossoff's party is rowdy, with hundreds packing the Crown Ravinia ballroom in Dunwoody as oldies and R & B tunes play in the background. Two giant screens are tuned to CNN, and huge roars erupt every time they show election results with Ossoff in the lead.

Long lines form at the cash bars and many in the crowd are enthusiastic, some a bit overly so. A few quiet skeptics are roaming the room, warning supporters that the long night is just beginning.

Meanwhile, the Karen Handel watch party in Roswell is a quiet affair with a cash bar and a few eats . The one flourish is on the small linen-covered tables. On each one, beneath a bouquet of white carnations, is a strand of pearls. Handel wears them, and has been mocked during the campaign for doing so by one of her male GOP rivals, former state senator Dan Moody. So it's something of a statement.

Overall, Handel's party is small, and absent any high-powered Republicans. Two Cobb County commissioners, Roswell Mayor Jere Wood, and a state lawmaker made up the bulk of officialdom. This was not a high-money crowd.

Updated at 8:45 p.m. -- Dark signs for the GOP? 

Some more positive signs for Ossoff as early numbers begin to trickle in from Cobb. He's got 57 percent of that county's vote so far.

As expected, Cobb resident Judson Hill is leading the Republican side of the field in that county. Overall, former Secretary of State Karen Handel is beginning to pull away from the GOP pack.

Here's our latest takeout from the race.

At her election night party, Handel told reporters she was proud that the Republican side of the race has been "a competitive campaign."

"There was no coronation, which is what occurred on the Democratic side," she said, setting her sights on Ossoff. "Everyone brought great ideas and new perspectives to the table and I appreciated that."

Meanwhile, Republican political consultant Chip Lake is beginning to project some dark signs for the GOP:

Updated at 8:00 p.m. -- First results 

Roughly an hour after polls closed, the first batch of election results were posted to the Georgia secretary of state's website.

Some early numbers from north DeKalb are positive for Ossoff, who netted more than 71 percent of the nearly 10,000 votes counted. The Democrat was expected to do well in the county, which constitutes the eastern, bluest portion of the 6th District.

Another encouraging tidbit for Ossoff, courtesy of Todd Rehm over at GaPundit:

Handel leads the early Republican field, closely followed by former state Sen. Dan Moody.

Plenty more to come.

Updated at 7:23 p.m. -- Handel's arrival 

Republican candidate Karen Handel arrived at the hotel for her watch party at 7:08 p.m. In a brief conversation with a reporter, Handel expressed confidence in her chances for making a June 20 runoff. Also in attendance: Rob Simms, her former chief of staff when Handel was Georgia's Secretary of State. Simms is the former executive director of the National Republican Congressional Campaign in D.C.

One more nugget: apparently today is Handel's birthday.

Updated at 7:00 p.m. -- Polls closed

Polls have closed everywhere outside of two precincts in Fulton County.

Check out our earlier post on what happens to the ballots after they're cast.

We'll be keeping tabs on the returns, but you can also follow along here.

Updated at 6:15 p.m. --  Reading the tea leaves

Political analysts are getting wound up about a pair of Sandy Springs districts that could signal a stronger-than-expected Democratic turnout.

The first is a precinct that Democrat Michelle Nunn won with 78 percent of the vote in 2014, meaning that it's a trove of potential votes for Democrat Jon Ossoff. Turnout in that precinct has nearly doubled on Tuesday, an astounding feat for a special election.

The second is a precinct in a more conservative stretch of Sandy Springs where Nunn only got about a third of the votes. Turnout there is only about half of what it was in 2014.

"That ain't good," texted one GOP operative.

Updated at 6:00 p.m. -- 6th District geography  

The 6th District encompasses portions of three counties: north Fulton, east Cobb and north DeKalb. Here are a few things to keep an eye on as vote tallies begin to come in.

North Fulton will likely account for the biggest chunk of the vote, in part because of the city elections that will also be on the ballot. It's also some of the most conservative turf in the district. Top Republican contenders Handel, Moody and Bob Gray all hail from there and will be duking it out for the county's allegiance. This county has a reputation for being slow to tally its votes, and two factors tonight indicate it could take longer for Fulton to report: the municipal elections and a judge's decision to let the county keep two precincts open past 7 p.m. tonight after encountering problems.

As we told you this morning, north DeKalb accounts for the most Democratic-leaning part of the district. It's where Ossoff grew up, and it's also where he'll be looking to rack up votes. There were also fewer early voting sites in that county, which could prompt a turnout spike today. No voting issues have been reported there so far.

The race's only top candidate to hail from east Cobb, former state Sen. Judson Hill, has struggled to build a sense of momentum in the contest. But there's an eight-candidate race to replace him in the legislature that's also on the ballot, which could help drive some turnout. Yesterday, state officials announced they were investigating the theft of voter check-in equipment from a Cobb County precinct manager's car that they warned could make every Georgia voters' personal information vulnerable to theft.

Updated at 5:00 p.m. -- Breaking down early voting 

As we wait for polls to close, let's break down what we know about the ballots that were cast ahead of time. Nearly 55,000 people voted early, mostly in-person but some absentee. And whereas early numbers showed Democratic front-runner Ossoff with a notable lead, Republicans appeared to catch up as more early voting sites opened.

The Upshot's Nate Cohn estimates that at the end of the day, early and absentee voters were "split evenly between the two parties, each at 41 percent, based on whether voters had last participated in a Democratic or Republican primary." At the same time, he warns that relying on early voting numbers alone is likely misleading. For starters, Republican voters had far more candidates to sift through, so many may have held off on voting until today.

What we do know is that early numbers are good for gouging voter enthusiasm. It's clear that Democrats are more riled up than they have been in years. As Cohn notes, their numbers are much higher than early voting in the 6th District midterms in 2014. The last time a special election was held in the same congressional district in 1999, it drew more than 79,200 voters.

Donald Trump, meanwhile, has now weighed in on the race for the sixth time in the last three days on Twitter.

The AJC's Michelle Baruchman contributed to this report.