Ulster (3) 13
Try: Danielli Con: Schifcofske Pens: Schifcofske (2)
Ospreys (6) 16
Try: Tiatia Con: Hook Pens: Hook (3)
James Hook of the Ospreys is stopped by Ryan Caldwell and Robbie Diack
Ulster slumped to a disappointing home defeat to a virtual second string Ospreys side in their penultimate home fixture in the Magners League.
When their Scottish winger Simon Danielli scored a 67th-minute try, Ulster were 13-6 ahead.
But they quickly conceded a third James Hook penalty and then the Welsh side charged over for a Filo Tiatia try awarded by the video official.
It was a fourth defeat in five Magners League matches for the Irish province.
The Ospreys, winning their fourth straight league fixture, remain third in the league standings.
The severely depleted visitors had the best of the early exchanges with two Hook penalties putting them 6-0 ahead after the first quarter.
Schifcofske landed Ulster's only score of a dreary first half with a penalty in the 28th minute.
After the break, The Ulster full-back was short with a kickable attempt and then pushed another penalty wide of the posts.
Three minutes later, though, Schifcofske finally made sure from a more favourable angle to level the scores.
Then came the Ulster try as Niall O'Connor launched a cross kick which sat up nicely for Danielli who dived under the posts to give Schifcofske the straightforward conversion.
The lead was cut by Hook when Ulster were penalised from the restart and, from there to the end, the Ospreys were on top.
Danielli just got to the ball to prevent a try when Jonny Vaughton's chip-and-chase nearly saw the winger get the touchdown.
But Ulster were pegged back in their own 22 and after a series of drives, Tiatia burrowed over and was given the score by the television match official.
Hook converted and Ulster could not threaten again over the last five minutes.
Ospreys boss Sean Holley:
"It shows we've got a lot a character and a tightness within this group. It shows we've got strength in depth.
"There's some great young talent coming through in our region and they've come to a really difficult place like Ravenhill - as any coach will tell you - and it's a fantastic win so I'm really pleased.
"That was the plan - to keep the pressure on the top two [Leinster and Munster] and we'll see how they thrash it out against each other.
"And now it gives us something really to challenge for going into the end of the season.
"It wasn't easy. It was very difficult - a big aerial assault and [I'm] really proud of not just those youngsters, but some of the stalwarts as well.
"It was a real team effort this week."
Ulster: Schifcofske, Danielli, Cave, Wallace, Trimble, O'Connor, Boss, Young, Best, Botha, O'Donoghue, Caldwell, Henry, Pollock, Diack.
Replacements: Brady, Court, Del Fava, Faloon, Willis, Whitten, Nagusa.
Ospreys: Owen, D. Bishop, Spratt, A. Bishop, Vaughton, Hook, M. Phillips, James, Bennett, Griffiths, A. Jones, Lloyd, Smith, Tandy, Tiatia.
Replacements: Hibbard, Bevington, Levi, Holah, Nutbrown, Biggar, Parker.
Referee: Peter Allan (Scotland)