The North did not have it all their own way though as they recovered from a 13-6 deficit with just five minutes of the game remaining.
Fly-half Callum Hall gave the North a 6-0 lead inside the first quarter with two penalties but Ospreys' scrum-half Matthew Aubrey responded with two kicks of his own as the teams went in level at half-time.
The home side had a number of opportunities to take control of the game but nearly an hour had passed before wing Rhys Gealy crossed to give the Ospreys the lead. Captain Owen Watkin added the conversion to give the Ospreys 13-6 advantage but with victory in sight, a lapse of concentration in defence allowed Blues North No. 8 Morgan Sieniawski to cross for a try.
Replacement Jacob Lloyd added the conversion to bring the sides level at 13-13 and with just minutes left, Lloyd kicked a penalty to earn the Blues North their second successive victory of the campaign.
At Parc y Scarlets, first-half tries from winger Rodgers and fly-half Fish were enough for a South win in a low scoring game with the Scarlets.
The South, with their large and powerful pack, controlled the first half with the Scarlets' game blunted by numerous handling errors.
Using their forwards to their advantage, both Blues' tries came from powerful driving mauls which allowed their backs to score wide out.
Finding themselves 10-0 down, the Scarlets responded with a try from wing Steffan Price after No. 8 Steffan Taffestauffer secured possession, ran 60 metres and fed Price who scored wide out.
With a five point lead at the interval, the South were looking to pull further clear but a stop-start second period did neither side any favours.
The referee's whistle played a big part and at one point the South were reduced to 13 players but they hung on for the victory despite failing to score after half-time.
Scarlets' wing Kieran Jones kicked a penalty but then missed a penalty which would have given his side the lead and the match in the dying minutes as the South held on.