With the table-topping Blues North sitting out of this week’s games, the Ospreys assumed top spot with a 38-13 victory.
Tom Prydie, Bowdy Davies (2), Adam Collins and Ryan Jones (2) crossed for tries with fullback Prydie adding four conversions.
Having lost only once this season, the Ospreys were always in control of a game which saw them lead 19-6 at the interval.
A second half try for Scott Curtis and two penalties and a conversions for Diggy Bird provided some consolation for a Blues South side who now need to win their remaining games to reach the final.
