Isn't that almost impossible? AFAIK the votes were approximately split 3 ways across 2 republicans and 1 democrat. That's the only reason why the democratic candidate was even ahead.
No, there are 2 senate races, and each had a Republican and a Democrat as top two vote-getters. In one race, the Republican came on top and in the other the Democrat did, but neither winner reached the 50% threshold required by state law, so both races are going to runoff.
In the race the Democrat was leading, the Republican candidate had a history of minor (local) scandals, and only held the seat because she was appointed to it.
In the special election, the top 3 candidates (two republicans and one democrat) got ~80% of the vote. There were a lot of other democratic candidates that got a total of ~15% of the vote, so it's plausible that Warnock (the democratic candidate in the runoff) could win.
Well that was the case pre-2016 election. 2017-2020 Democrats did very well in special elections. It remains to be seen what happens to democratic enthusiasm under a Biden presidency.
In the race the Democrat was leading, the Republican candidate had a history of minor (local) scandals, and only held the seat because she was appointed to it.