Victories for the Blues and Scarlets threw wide open the race for a place in the final of the WRU Under 18 Age Grade Championship.
Although it was the Ospreys who went into the third round of matches with a 100 per cent, it was a case of all change as the Scarlets defeated the Dragons at Stradey Park and the Blues were successful at the Ospreys.
Elliott Jones and Harley Thompson crossed for the Blues who had Diggy Bird to thank for their remaining points two conversions and three penalties.
The Ospreys, who led 13-9 at the interval courtesy of a Ben Thomas try and a conversion and two penalties from Tom Priday, were outplayed in the second half and eventually went down 23-13.
First half tries from Jack Roberts, Aled Davies and Tomos Ellis Williams put the Scarlets on course at Stradey Park and Kirby Myhill made sure of a bonus point in his sides 38-18 success. James Russell added three conversions and a penalty and Dale Ford three penalties.
Lewis Roblin with two penalties and a conversion, finished with eight points whilst there were tries for Aledc Cooper and Nicky Williams.