Blues North under 16s brought to an end the Ospreys' unbeaten run in the WRU Age Grade Championship and at the same time registered their first victory of the season.
After kicking off the campaign with defeats against the Dragons, Scarlets and Gogledd Cymru, the North edged out the Ospreys 19-17 in a real thriller at Pontypridd's Sardis Road.
Centre Callum Phillips, Joel Riggs and Josh Flye bagged tries for the hosts with Phillips and James Dixon adding a conversion apiece.
For the Ospreys, there were tries from Ryan Evans and Nicky Smith whilst Dan Thomas and Sam Davies added conversions and Thomas a penalty.
Team manager Nigel Way said; "we haven't been far away in our other games, but credit to the boys for sticking with it and coming away with a first win of the season."
Having started the season so brightly, defeat means the Ospreys slip further behind runaway leaders the Scarlets who defeated the Dragons 36-16 at the Recreation Ground, Tredegar.
With three victories under their belts already, the Scarlets bagged another bonus point in beating the Gwent region by four tries to two.
Jake Randall and Thomas Ball crossed for tries in the first half as the visitors swept into a 21-8 interval lead.
After that, it was a straightforward evening for the Scarlets as Sion Bennett and Dylan Morgan crossed for tries number three and four.
Jordan Williams, who went into the game with 55 points, kicked four penalties and two conversions as the Scarlets eased to another consummate victory.
Michael Adams and Dominic Franchi scored tries for the Dragons with Ethan Davies adding two penalties.