ATLANTA (AP) — As votes were still being counted Thursday in Georgia, results for Republican U.S. Sen. David Perdue hovered near the threshold where a runoff against Democratic challenger Jon Ossoff would be required.

Perdue led unofficial returns as he sought a second term, but Ossoff still hoped to narrow the margin as votes continued to come in from Democratic-leaning areas. The Associated Press has not yet called the race.

“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 in a statement.

Ossoff’s campaign manager, Ellen Foster, said in a statement that the campaign is “confident that Jon Ossoff’s historic performance in Georgia has forced Senator David Perdue” into a runoff.

In Georgia, a candidate must win more than 50% of the vote to avoid a runoff.

Republican Secretary of State Brad Raffensperger said Thursday afternoon that there were thousands of ballots left to be counted. There are also provisional ballots and ballots that need to be “cured” before being scanned, and ballots cast by military voters and citizens living overseas can be received through 5 p.m. Friday and still be tallied.

Many of the outstanding ballots left to be tallied were in Democratic strongholds in metro Atlanta and Chatham County, which contains Savannah.

Georgia’s other U.S. Senate race is headed to a Jan. 5 runoff between GOP Sen. Kelly Loeffler and Democrat Raphael Warnock.

The dual races could help determine control of the chamber.

Democrats haven’t won a Senate race in Georgia in two decades, but Republican dominance in statewide races has been slipping in recent elections.