A bonus point win over Ulster means the Ospreys go into Christmas at the top of the PRO12 table.
Rhys Webb bagged two tries while Dan Biggar and Hanno Dirksen scored one apiece, Biggar adding 11 points with his boot.
The Ospreys were ahead inside three minutes, Biggar getting the scoreboard moving nice and early with a simple penalty from the 22m line.
Ulster settled into the game after that and after enjoying the upper hand in terms of possession and territory they were level on 15 minutes, Ian Humphreys with the penalty after Josh Matavesi came into the ruck from the side.
That score sparked the Ospreys into life and they grabbed the opening try within two minutes. It was a length of the field score, and a lesson in keeping the ball alive, the move sparked by Eli Walker collecting the ball in his own 22 under pressure from Darren Cave before feeding Dirksen. The ball was swiftly moved upfield and it was Alun Wyn Jones who provided the scoring pass for Biggar to go under the posts before picking himself up to convert.
Buoyed by that score, and aided by some poor kicking out of hand from Ulster, the Ospreys were putting together some nice moves with Dirksen and Dan Evans both prominent, but desperate Ulster defence ensured they kept their line intact.
It was a poor clearance kick from Humphreys that allowed the Ospreys to come back at the Ulster line and some lovely rugby stretched the defence to breaking point until, eventually, it was Rynier Bernardo who broke the line before releasing Webb for his 8th of the season, Biggar adding the extras two minutes before the interval.
There was still time for Ulster to come back, a high tackle by Eli Walker allowing Ulster to go for the corner. Their rolling maul was halted, Cave knocked on, the Ospreys tried to run it only for Evans to lose possession, and Humphreys crossed for the visitors.
Referee Neil Paterson originally awarded the try before being convinced to review the video evidence. Cave’s knock on was obvious but the ref insisted that the advantage was over by the time Evans lost the ball only for touch judge Nigel Owens to intervene, highlighting Alun Wyn Jones’ knock on off Cave’s initial knock on, meaning that he couldn’t play advantage and finally, after much confusion, the score was chalked off much to the delight of the home crowd.
HALF-TIME: OSPREYS 17 ULSTER 3
An early scrum penalty in Ulster’s favour allowed the visitors to strike first after the break, Humphreys successful with his second kick of the night.
The Ospreys struck back in some style, grabbing their third try on 48 minutes. Matavesi made the line break, Justin Tipuric fed Walker and when the ball went to ground Tipuric reacted first and sent Webb over, the TMO checking for a knock-on by Walker before awarding the score. Biggar’s conversion took it to 24-6.
It got better on 55 minutes when Dirksen went over for the bonus point try, cutting infield at a great angle to take Webb’s pass from a scrum five before being driven over the line by Webb and Tipuric. Again, Biggar converted.
Ulster served notice that they wouldn’t go down without a fight and a lineout drive on the hour saw Rob Herring crashing over for their first try, Humphreys converting, making it 31-13 going into the final quarter.
Seven minutes later it was former Osprey Tommy Bowe who crossed the Ospreys line after a scrum penalty saw Ulster go to the corner again. Although their drive failed to find any momentum this time, Bowe’s angled run scythed through the defence for him to score under the posts, Humphreys again with the conversion.
The Ospreys were able to professionally see out the final minutes without too much difficulty, securing their eighth PRO12 win in ten games.