Debutant wing Dean Williams opened the scoring with an excellent firts half try and second half scores from the outstanding Ashley Beck and replacement hooker Matthew Lilley secured the victory points. Biggar added a second half conversion and penalty to round off the victory and leave the Ospreys on top of the tree with maximum points. Sam Shelley scored the Blues North try and Harry Alan added a penalty.
The U18 are also unbeaten after two games - they came from behind at Caerphilly to defeat the Dragons 13-11.
Richard Cunniffe, who scored eight points in the defeat of the Scarlets on the opening day, bagged a penalty five minutes before the interval, but with 10 minutes remaining, the Ospreys trailed 11-3 with Gareth Dare (try), David Langdon (pen) and Jason Tovey (pen) leaving the Dragons in good shape. However, Rhys Lawrence closed to the gap to three points with his side's first try and Lee Halfpenny nipped over three minutes later to secure the spoils.
In the other U18 game, the Scarlets pipped the Blues 33-30 with Daniel Evans, Gruff Jones (2), Josh Turnbull grabbing tries and Evans adding 13 points with the boot. The Blues also scored four tries - Matthew Edwards, Rhys Dyer, James Toller and Tom Price were on the mark with James Thomas kicking 10 points from two conversions and two penalties.
The Scarlets U16 managed a try from Gareth Flynn and a Daniel Etteridge penalty in their 13-8 defeat at Blues South, but the home side won the day with a try from Cory Hearn and eight points from Luke Fear.
Ospreys 25 Blues North 8
Tries: Williams, Lilley, Beck
Conversions: Biggar (2)
Penalties: Biggar (2)
Blues South 13 Scarlets 8
Penalties: Fear (2)
Dragons 11 Ospreys 13
Tries: Lawrence, Halfpenny
Scarlets 33 Blues 30
Tries: Evans, Gruff Jones (2), Turnbull
Conversions: Evans (2)
Penalties: Evans (3)
Tries: Edwards, Dyer, Toller, Price
Conversions: Thomas (2)
Penalties: Thomas (3)