Cardiff Blues lost their stranglehold over Ulster, which stretched back seven games to October, 2006, as they were beaten 37-15 at home in the Magners League.
The Blues were leading 15-8 at the break thanks to tries from Casey Laulala and Tom James, but then fell apart in the second half as they conceded four tries and 29 unanswered points.
Ulster's teenage wing Craig Gilroy scored a try in each half and his second touchdown, which began at a quickly taken line-out in the visitors' 22, turned the game on its head.
It also came in the middle of a 15 point burst from Ulster in the space of four minutes and set them on their way to a first bonus point victory of the season.
The defeat means the Blues lose their grip on third place in the Magners League table, Ulster moving ahead of them, and puts added pressure on next weekend's home clash with Glasgow Warriors.
Earlier in the weekend a last gasp try from replacement scrum half Jamie Nutbrown earned the Ospreys an important 16-15 victory over Connacht in Galwey. That triumph included a drop goal from the 18-year-old Matthew Morgan on his Magners League debut.
But there wasn't any luck for the Dragons in Ireland as they conceded four tries in a 27-6 defeat against Leinster in Dublin.
Whenever Bedlinog tackle Penallta a massive fixure is guaranteed but this Sunday there will be even more emphasis placed on the two rivals when they contest the SSE Swalec Plate final at Principality Stadium.
Ahead of their SSE SWALEC Bowl Final clash with Taffs Well at Principality Stadium on Sunday, Burry Port share their #FABXV nomination with WRUTV in the search for Welsh rugby's greatest volunteers. Everyone can get involved by sending nominations via twitter to @WRU_Community using the hashtag #FABXV
Cardiff Blues prop Gethin Jenkins and Ospreys centre Ben John look ahead to the first game at Principality Stadium in Saturday's double header which is promising to be a special occasion for all Welsh fans.
Carmarthen Quins Director of Rugby Ian Jones and committee member Jeff Thomas along with Llandovery chairman Handel Davies look ahead to Sunday's SSE SWALEC Cup showdown where both teams are out to prove 'West is best'
SWALEC ambassador Shane WIlliams is looking forward to Sunday's Finals Day where the Cup, Bowl and Plate offers a great opportunity for players and teams to experience the magic of playing at Principality Stadium
Carmarthen Quins coach Richard Kelly believes it is an exciting time to be part of the Scarlets region as his side take on local rivals Llandovery in the SSE Swalec Cup final on Sunday, as WRU TV's Graeme Gillespie discovers