Ulster winger Tommy Bowe is tackled by Mark Taylor of the Ospreys
Ulster (8) 8
Ospreys (6) 16
Pens: Hook (3)
The Ospreys overturned a half-time deficit to secure an important Heineken Cup Pool Two victory at Ravenhill.
Ulster, beaten 48-17 away to the Ospreys a week earlier, produced a much better display and led 8-6 at the break with Simon Danielli scoring a try.
But the Welsh outfit stunned Ulster with a fine 52nd-minute response.
In a well-rehearsed line-out routine, number eight Filo Tiatia fed fellow Kiwi Justin Marshall and the scrum-half ran through for a match-winning try.
James Hook's conversion made it 13-8 to the visitors.
Ulster fought hard to find a scoring response but were hampered by two yellow cards in the second half.
Ryan Caldwell was the first to go for deliberately preventing the ball coming out of a ruck.
Soon after he had returned to the fray another lock, Italian international Carlo Del Fava, was sin-binned for hair-pulling.
The Welsh club opened a six-point first-half lead through two Hook penalties before Ulster's young fly-half Niall O'Connor, making his first Heineken Cup appearance, reduced the deficit to three points with a 17th minute penalty.
Danielli gave Ulster an unlikely lead thanks to a strong run to the left corner from Tommy Bowe's short pass.
The try sparked hopes that Ulster, beaten in their first three pool matches and bottom of the Magners League, could produce a shock result.
Their defensive work was much improved from the heavy defeat at the Liberty Stadium.
But Marshall's try, a perfectly executed training ground move, silenced the Ravenhill crowd.
Fly-half Hook landed the subsequent conversion and added a penalty to make it 16-8.
Ospreys coach Lyn Jones:
"We came here to win. We played really well last week but we're still in the tournament.
"We were under no illusions about coming here and we're really delighted to get that win.
"We knew how tough a game it was going to be and I was really impressed by Ulster's performance and by the crowd who really got behind their players."
Ulster caretaker coach Steve Williams:
"Last week we let ourselves down and took a step backwards but tonight we got at them and said we'd fight for every ball.
"We stuck at them tonight and got in their faces. We probably had a couple of chances we didn't finish off.
"When we were direct we looked effective and if we play like that we will win games."
Ulster: Cunningham, Bowe, Trimble, Dewey, Danielli, O'Connor, Campbell, B. Young, R. Best, D. Fitzpatrick, Harrison, Caldwell, N. Best, Dawson, McCullough.
Replacements: P. Wallace for O'Connor (56), Boss for Campbell (56), Court for D. Fitzpatrick (72), del Fava for Harrison (66), Pollock for Dawson (61). Not Used: Miles, McCrea.
Sin Bin: Caldwell (55), del Fava (68).
Ospreys: Byrne, Walker, Taylor, Parker, S. Williams, Hook, Marshall, D. Jones, Bennett, A. Jones, Wyn-Jones, Evans, Thomas, Holah, Tiatia.
Replacements: Connor for Hook (72), Phillips for Marshall (72), Hibbard for D. Jones (75), James for Bennett (75), Gough for Evans (75). Not Used: T-Pole, A. Bishop.
Referee: Malcolm Changleng (Scotland).