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.
Cardiff Blues were crowned the Welsh champions of the Premiership Rugby 7s Series on Saturday night to book a place at the Series Final on Friday, August 8 - and you can join them with tickets on sale NOW!
Wales will tonight (Saturday) stage the first leg of the Premiership Rugby 7s Series this Saturday evening at the BT Sport Cardiff Arms Park - and tickets remain on throughout the day and right up until kick-off so you can join us for an summer night of top class rugby!
In its sixth year the Blues Cup once again showed to be huge hit throughout the region and is a great advert for the community game as each of the six finalists across the three age groups produced rugby of an outstanding level resulting in 14 tries.
Inspired Cardiff Blues enjoyed Judgement Day at the Millennium Stadium as they secured a tense 17-13 win over regional rivals Scarlets in a feisty and enthralling encounter in the RaboDirect PRO12 on Easter Sunday.