Ulster were controversially denied a late try at Electric Brewery Field in Bridgend as Ospreys dug out a 21-10 win in the United Rugby Championship.
The Welsh side – looking to make it five URC games without defeat – had made a fast start, with Cormac Foley slipping in for the opening score after just three minutes following a line-out and Jack Walsh sending over the conversion.
Ulster, though, soon mounted a fightback to turn the match around with two quick tries of their own.
First, a kick into the corner from Nathan Doak found Zac Ward, who dived over for an instant response in the ninth minute and Tom Stewart then went over off the back of a rolling maul.
Doak, though, again failed to land the extras leaving Ulster with a slender 10-7 lead to take into half-time.
The early part of the second half proved a scrappy affair, with both sides giving away possession, and Ospreys out-half Jack Walsh was sent off for a head injury assessment amid a flurry of replacements.
Ospreys eventually found another gear to mount a sustained period of possession, which saw James Ratti go over off the back of the pack in the 68th minute and Walsh added the extras to put the home side ahead by four.
Ulster thought they had gone back in front at 15-14 with six minutes left when Angus Bell dived over through a sea of bodies on the line.
However, a lengthy review by the TMO eventually resulted in a yellow card for Marcus Rea, who was deemed to have made a dangerous clearout with his shoulder to Owen Watkin's head while he was on the ground.
