Former Georgia gubernatorial candidate Stacey Abrams, and founder of Fair Fight, sent an encouraging tweet to supporters moments after Warnock took the lead over Loeffler in his Senate race with 95% of the expected vote reporting in.

“With new votes joining the tally, we are on a strong path. But even while we wait for more, let’s celebrate the extraordinary organizers, volunteers, canvassers & tireless groups that haven’t stopped going since Nov. Across our state, we roared. A few miles to go...but well done!” Abrams tweeted.

Gabriel Sterling, the state voting system implementation manager, said at an earlier election update that the largest portion of remaining uncounted votes was out of DeKalb County, a heavily Democratic suburban Atlanta area.

Gabriel Sterling, the state voting system implementation manager, said in an evening election update that the largest portion of remaining uncounted votes is from DeKalb County, a heavily Democratic suburban Atlanta area.

"The biggest tranche of votes that exists out there in a single bucket right now still looks to be the advanced voting in DeKalb County," Sterling said.

With 80% of the expected vote reporting in, GOP candidates Perdue and Loeffler are leading their races by small margins.

Sterling said from the press conference in Atlanta that he wasn't aware of any issues that could delay the reporting but added, "It can be like seesaw for the rest of the evening."

Sterling said 64 of the state's 159 counties have completed reporting all votes.

-ABC News' Quinn Scanlan

Georgia Lt. Gov. Geoff Duncan, a Republican, told ABC News Live he's worried that President Donald Trump's baseless allegations of election fraud in the state "absolutely" might have depressed GOP turnout in the runoff races.

"Unfortunately, too many folks in our party over the last two months have been talking about misinformation, election fraud and creating a distraction," Duncan said.

"We've been outworked, out-focused, but my hope is that Kelly Loeffler's and David Purdue's hard work over the last two months is going to get them across the finish line and help us kind of regroup as a party here in this state, and also as a country, and be able to roll back out and get the White House in 2024," he added.

ABC News Chief Congressional Correspondent Mary Bruce stressed the significance of Tuesday's runoffs, not only because they will determine control of the Senate but because they leave President-elect Joe Biden's agenda hanging in the balance.

"It's not just how much he can get done but also the expediency with which he might be able to get things done," Bruce said, outlining big promises in Biden's agenda, from health care to climate change.

Biden has noted in recent days, while stumping for Democratic candidates, that if Democrats are able to win both seats, the $2,000 stimulus checks Democrats have been pushing for could happen immediately. Also, the approval of additional aid to state and local governments and resources to distribute the coronavirus vaccine in a more timely fashion could come quickly.

"Not to say that Joe Biden's agenda would hit a complete brick wall if Republicans continue to maintain control in the Senate because, of course, Joe Biden prides himself on having a great working and personal relationship with Republican leader Mitch McConnell, but it certainly would make Joe Biden's agenda and his political ambitions here much, much, much easier," Bruce said.

Bruce also noted how the expected efforts by Republicans to object to the certification of the Electoral College results on Wednesday could give the public a sense of the "uphill battle" Biden may face if the GOP does maintain control of the Senate.

Walter Jones, a spokesperson for the Georgia secretary of state’s office, shared certification deadline information with ABC News Wednesday for the runoff elections.

If Ossoff wins, and the results aren't certified until the deadlines below, then President-elect Joe Biden won't have a majority in the Senate until a few days after his inauguration.

If the results are certified and the Democrats are seated before Biden takes office, Democrats won't have a majority until he's inaugurated because they need Vice President-elect Kamala Harris as the tie-breaking vote.

The deadlines are as follows.

Friday, Jan. 8: The deadline to cure rejected absentee ballots, deadline to verify provisional ballots (if voters lacked photo ID), and deadline for receiving military/overseas ballots postmarked by Election Day.

Friday, Jan. 15: The deadline for counties to certify election results (though this could happen sooner if everything is ready).

Friday, Jan. 22: The deadline for the secretary of state to certify election results (this also could happen sooner if everything is ready).

The deadline for a campaign to request a recount if the margin is less than 0.5% is two business days after the secretary certifies the election. If the secretary does this on Jan. 22, then a campaign would have until Tuesday, Jan. 26 at 5 p.m. to put in the request.

Georgia code says the secretary delivers the vote totals to the governor who issues a certificate of election to the winners

-ABC News’ Quinn Scanlan