The Senate race in Georgia is going to a runoff, just as it did in 2020, and it may decide the balance of power in the upper chamber, just as it did in 2020.

The final tally had the Democratic nominee, Senator Warnock, leading the Republican nominee, Herschel Walker, by 49.4 percent to 48.5 percent. Because Georgia requires a candidate to receive more than 50 percent of the vote to win, the state will have a runoff election on December 6.

In 2020, Mr. Warnock won the seat after defeating the incumbent Republican, Senator Loeffler, in a high-stakes runoff. Another Democrat, Senator Ossoff, won Georgia’s other Senate race that year, and thus control of the Senate was delivered to their party.

A professor of political science at the University of Georgia, Charles Bullock, suspects that a runoff in the mold of the 2020 election would be a net benefit to Senator Warnock.

Mr. Walker’s election performance was helped by Governor Kemp at the top of the ticket, he said, and with no other elections on the ballot, Republicans who have reservations about the former football star may just stay home.

On the other hand, Mr. Warnock himself appeared to drive turnout on the Democratic side, outperforming the Democratic nominee for governor, Stacy Abrams.

“In this runoff the only item on the ballot is the runoff, and if you don’t care that much about that you’re not going to show up,” Mr. Bullock tells the Sun.

Democrats have been quick off their blocks in announcing spending and resources headed toward their nominee in Georgia. The Democratic Congressional Campaign Committee has already said it will be investing some $7 million into the party’s ground game there.

“We know talking directly to voters through a strong, well-funded ground-game is critical to winning in Georgia, and we’re wasting no time in kick-starting these programs in the runoff,” said the Democratic Senatorial Campaign Committee chairman, Senator Peters.

The same committee, a major Democratic political action committee, made a big bet on its field and voter contact operations during the general elections, an effort that appears to have paid off. 

The committee spent some $60 million on field efforts on top of $53 million on independent expenditures like television and digital advertising. Before the election Mr. Peters said the “strategic investment” had “helped put Senate Democrats in the strongest position possible.”

Mr. Warnock’s campaign manager, Quentin Fulks, has also begun to position the senator as the favorite to win the runoff, touting his previous runoff victory, the party’s formidable ground game, and Mr. Warnock’s record in the Senate.

Mr. Fulks also has called into question Mr. Walker’s ability to win based on his performance in the general election, writing that “Herschel Walker underperformed in an environment that set him up for success.”

“Not only did Walker underperform Governor Kemp, he earned fewer raw votes than every single Republican on the ballot,” Mr. Fulks wrote. “Of nine statewide Republican candidates, Walker was one of only two who failed to clear two million votes.”

He also suggested that voter turnout is a foreboding sign for Mr. Walker, who underperformed President Trump’s 2020 performance in suburban and urban counties.

The Republican infrastructure has been slower to react than the Democrats, with a representative of the Senate Leadership Fund telling the Sun that it has no news to announce as of yet.

In Georgia, however, Mr. Walker’s campaign has announced that it has banked $3.3 million in donations on the first day of the runoff campaign.

Mr. Walker appeared on Fox News in an effort to display confidence in his position, arguing that the race in Georgia will decide control of the Senate.

“Right now we’re in a tiebreaker and that’s why I said I’m not giving this seat up, because right now the Georgian people are hurting,” Mr. Walker said. “They’re going to throw more at me — even the kitchen sink — but I can catch it.”

As of Thursday, there are still two outstanding Senate races, in Arizona and Nevada, that will bear on which party controls the upper chamber from January.

In Arizona, it’s looking like Senator Kelly will win another term, as he is leading the Republican nominee, venture capitalist Blake Masters, 51.4 percent to 46.4 percent with 70 percent of the vote reporting.

In Nevada, the Republican attorney general, Adam Laxalt, currently leads the Democratic incumbent, Catherine Cortex Masto. Unlike in Arizona, there is an expectation among some that Ms. Masto will catch up as the remaining vote is counted.

An editor of the Cook Political Report, Dave Wasserman, said Democrats have a good shot of taking control of the upper chamber before the runoff in Georgia begins in earnest.

“After last night’s Nevada mail ballot trend, there’s an excellent chance now that Democrats will have 50 Senate seats/control in hand heading into the Georgia runoff,” he said in a tweet on Thursday.

In Mr. Bullock’s opinion, either party winning both Arizona and Nevada would probably stand to benefit Mr. Warnock, given the lack of enthusiasm for Mr. Walker in Georgia.

“If either party wins both of these then Georgia becomes an interesting side show — it’s not critical it’s not decisive,” Mr. Bullock tells the Sun. “Either way it probably helps Warnock and the reason is that a number of Republicans are concerned about Herschel Walker.”

Correction: Senator Ossoff is the other Democrat who won in Georgia in 2020. The lawmaker was misidentified in an earlier version.