That's the record for Democrats in winning open-seat Senate races in the "real" South (not including Florida, but including Kentucky and Oklahoma) since 1987 (I count the Texas special in 1993 as an open seat, although Bob Krueger was a nominal incumbent). Democrats have occasionally knocked off inept Republican incumbents (Lauch Faircloth, Tim Hutchinson), but they have become spectacularly bad at winning races in Dixie without an incumbent, when national forces tend to be most prominent.
So much of Democratic strength in the South has been based on inertia: the clout of powerful incumbents like Lloyd Bentsen and Sam Nunn; the ancestral loyalty of older, rural voters; control of redistricting; business interests' understandable desire to get along with the normal governing party; potential Republican candidates unwillingness to be part of an embattled minority in state legislatures.
Above all else, generations of politicians with conservative values and a practical bent had assumed that the Democratic Party was the only way to get ahead. That's over.