The neighbours put more than a century of bitter rivalry behind them to launch the Celtic League with a rare Welsh victory over Irish opposition.
Gavin Henson, snubbed by Steve Hansen for the World Cup, came off the replacements bench to prove a major point by scoring two tries in the final eight minutes to clinch a win and a bonus point for the Ospreys.
Captain Scott Gibbs, returning to the ground where he began his career 14 years ago, revelled in the occassion and after a trademark barging run, supplied the scoring pass for wing David Tiueti to cruise over within the opening two minutes.
Ulster, however, struck back with three counter attacking tries in the space of 12 in an open and entertaining first half.
Pressure up front forced Ospreys scrum-half Andy Williams into a wild pass that was intercepted by Ryan Constable to create the first for centre Shane Stewart. Pady Wallace broke from deep inside Ulster territory, followed up by Tyron Howe to send over prop Ronan McCormack while full-back Bryn Cunningham robbed Williams of possession, broke some lose tackles and sent captain Andy Ward galloping over from 30 yards out.
Nine points from the boot of Shaun Connor however kept the Ospreys in touching distance and when full-back Adrian Durston caught Ulster’s defence still in the changing room just a minute into the second-half, the initiative swung back into the Ospreys’ favour.
Connor and Wallace, who had barely got the ball off the ground with two earlier attempts, exchanged penalties as temperatures rose with the Ospreys just two points ahead.
Henson replaced Connor just after the hour mark and proved to be the match winner.
His pass released wing Elvis Sevalai’i and was then on hand for the return to drive over from close range with the help of prop Adam Jones and followed that with a second in injury time after booting a monster 40-yard penalty.