Joe Biden pulled within about 10,000 votes of President Donald Trump in Georgia early Thursday as election workers counted tens of thousands of absentee ballots, while U.S. Sen. David Perdue prepared for a likely January runoff against Democrat Jon Ossoff.

Trump’s once-formidable lead over Biden steadily shrank throughout the day as the count of mail-in ballots continued, giving Democrats a chance to carry Georgia for the first time in a White House race since 1992. Ossoff’s climb, meanwhile, raised the prospect of two Georgia runoffs that could decide control of the U.S. Senate.

Perdue fell slightly below the 50% threshold as ballots from metro Atlanta and Chatham County were tallied, and the Republican’s campaign said it was gearing up for another round of voting on Jan. 5, required by Georgia law if no candidate gets a majority of the vote.

“If overtime is required when all of the votes have been counted, we’re ready, and we will win,” Perdue campaign manager Ben Fry said.

Ossoff aide Ellen Foster said she’s confident the campaign “has forced Senator David Perdue to continue defending his indefensible record of unemployment, disease and corruption” in a runoff.

RELATED: Update on the vote count in metro Atlanta’s Fulton County

Georgia’s other U.S. Senate seat is already headed toward a Jan. 5 showdown, with incumbent Kelly Loeffler facing Democrat Raphael Warnock in the matchup.

The slow count put Georgia and a dwindling number of other battlegrounds in the spotlight as the undecided presidential race tightened with Biden flipping Arizona, Michigan and Wisconsin.

About 39,000 absentee ballots, mostly concentrated in metro Atlanta and Savannah, remained to be tallied. County election officials once promised to complete most of their counts Wednesday, but the timeline shifted to Thursday. There are also thousands of provisional ballots and military absentees to count over the next few days.

State elections officials say most of the counting of absentee ballots should be wrapped up Thursday, but they stressed that provisional ballots, military overseas votes and others won’t be tallied for days more. Gabriel Sterling, the state voting system implementation manager, urged Georgians to be patient.

“This is going to be an extremely close margin – especially in the presidential election,” he said, adding: “Fast is great. We appreciate fast. We more appreciate accuracy.”

The largest trove of absentee votes in the state that hadn’t yet been processed was in Chatham County, where about 17,000 ballots needed to be tallied. Several metro Atlanta counties had smaller batches of absentee ballots to process.

At stake are Georgia’s 16 electoral votes, which could be enough to give Biden the 270 votes needed nationwide to become president, according to counts by The Associated Press.

“I think it’s really close," said Deputy Secretary of State Jordan Fuchs, “and it could be as close as 1,000 votes.”