Democratic challenger Raphael Warnock won a hotly contested US Senate race in Georgia over Republican incumbent Kelly Loeffler, TV networks and Edison Research projected, but which party will control the chamber was up in the air with a second contest still undecided.
Warnock, a Baptist preacher, defeated Loeffler in one of two runoff elections in Georgia that will decide control of the Senate - and whether Republicans will be able to block President-elect Joe Biden's agenda.
The race between Democrat Jon Ossoff and Republican David Perdue was still too close to call.
With 98 percent reporting, Warnock was ahead of Loeffler by a percentage point, roughly 40,000 votes, while Ossoff led Perdue by about 3560 votes, according to Edison Research.
The critical races drew an estimated 4.5 million voters - a record for a runoff - along with nearly half a billion dollars in advertising spending since November 3 and visits on Monday by Republican President Donald Trump and President-elect Joe Biden.
Most of the votes remaining to be counted were in counties Biden won in November, with roughly 30,000 to go in DeKalb and Newton counties near Atlanta, according to Edison Research estimates.
"We were told that we couldn't win this election. But tonight, we proved that with hope, hard work and the people by our side, anything is possible," Warnock told supporters in a livestream message before the projection.
"I am going to the Senate to work for all of Georgia, no matter who you cast your vote for in this election."
Georgia Secretary of State Brad Raffensperger said election officials would take a break overnight but resume counting on Wednesday morning. "Hopefully by noon we'll have a better idea where we are," he said on CNN.
Democrats must win both contests to take control of the Senate. A Democratic sweep would create a 50-50 split in the Senate and give Vice President-elect Kamala Harris, as president of the Senate, the tie-breaking vote after she and Biden take office on January 20. The party already has a narrow majority in the House of Representatives.
If Republicans hold the second seat, they would effectively wield veto power over Biden's political and judicial appointees as well as many of his legislative initiatives in areas such as economic relief, climate change, healthcare and criminal justice.
No Democrat has won a US Senate race in Georgia in 20 years. The head-to-head runoff elections, a quirk of state law, became necessary when no candidate in either race exceeded 50 percent of the vote in November.
Warnock will become Georgia's first Black US senator and Ossoff, at 33, would be the Senate's youngest member. Perdue is a former Fortune 500 executive who has served one Senate term. Loeffler, one of the wealthiest members of Congress, was appointed a year ago to fill the seat of a retiring senator.