However, they are scheduled to play each other tomorrow morning at Rumney RFC (11am).
With the Ospreys and Dragons having established themselves in the top two positions after half a dozen rounds, victory, for both sides tomorrow, is essential.
The South go into the game fresh from an outstanding 21-15 victory over the Scarlets at Stradey Park - their third win in six games so far this term.
On the same night, the Blues North went down 30-5 to the table-topping Ospreys. However, they have already exceeded expectations this season with victories over the Scarlets and against tomorrow's opponents, 18-7, in October.
Tries from Matthew Howells, Rhys Williams and Daniel Lewis put the North on their way to a first victory in the competition with Gary Williams adding a penalty.
James Loxton bagged a try for the South, but they will need more than that tomorrow morning if they are to see off the North.