Three penalties from Ruan Pienaar and one from Stuart Olding proved not quite enough to overcome an inexperienced but dynamic Ospreys collective and, although Ulster still sit atop the table with a comfortable 10-point cushion over tonight's opponents, the team will be disappointed to have lost their 100% home league record at this stage of the season.

Although deprived of half a team's worth of players called up for Six Nations duty with Ireland, Mark Anscombe was nevertheless able to field a strong starting XV, bolstered by the return of captain Johann Muller to the second row, and Luke Marshall to the centre. Olding got his first full appearance at out-half, and young prop Andrew Warwick earned himself a berth on the replacements bench alongside, among others, the recently rehabilitated Dan Tuohy.

After a lively opening salvo from both teams, Ruan Pienaar kicked Ulster into a fourth-minute lead with the Ospreys penalised for not releasing their man in the tackle. This was cancelled out by Matthew Morgan's swerving kick five minutes later after an Ulster offside, but the same player was wildly off-target with a close-range drop goal attempt in the next Ospreys attack.

Pienaar added a second penalty from just shy of half-way on 13 minutes, but with the Ospreys playing the more adventurous rugby as the first quarter drew to a close, Ulster were lucky to escape without any further concessions, as a promising Welsh attack broke down with flanker Sam Lewis pulled up for holding on too long in the tackle.

The Ospreys came straight back, however, and Morgan was on-hand on 22 minutes to equalise once again with another penalty. Their next attack threatened to be even more lucrative, with several phases taking the visiting forwards to within a metre of the try-line, but the Ulster defence resisted obstinately, and Andrew Trimble was eventually able to clear after a hopeful prod forward from Morgan's boot.

Ulster mounted their first veritable attack on the half-hour, with good ground earned by Marshall and Paddy Wallace in particular, and swift recycling from Pienaar. Suddenly under intense pressure, the Ospreys infringed directly in front of the posts, with Joe Bearman failing to release ball-holder Michael Allen in good time, and Pienaar chipped over to make it Ulster 9 Ospreys 6 on 32 minutes.

With the balance of power now having swung in their favour, Ulster closed out the half in Ospreys territory, but taking into account possession and territory over the period as a whole, the hosts could count themselves fortunate to run off at the interval ahead on the scoreboard.

Half-Time Score Ulster 9 Ospreys 6

With Darren Cave replacing a hobbling Wallace minutes into the second period, the game pursued a somewhat disjointed rhythm, with the Ospreys again resorting to a drop goal attempt on 50 minutes - this time from scrum-half Kahn Fotuali'i - which went the same way as Morgan's had in the first half.

The out-half successfully kicked a penalty three minutes later, however, to level the score, but with an oft-misfiring Ulster lineout finally going right on 56 minutes, a strong drive from the forwards promised much before it was halted by the referee's whistle, once more for holding on too long in the tackle.

With Tuohy, Paul Marshall and Niall Annett all entering on the hour mark for Muller, Pienaar and Rob Herring, Ulster seemed re-invigorated, and were rewarded for five minutes of sustained pressure with a penalty in front of the posts, which also saw Ospreys Number Eight exiled to the sinbin for coming off his feet. Olding took over kicking duties in the absence of Pienaar, and calmly slotted over to re-establish the home lead.

However, the Ospreys threat which had been bubbling under for the entire match then came to a head, Ryan Bevington showing exceptional pace and stamina for a prop to collect Fotuali'i's angled pass from the wing and outstrip the chasing Ulstermen for the try. Morgan added the extras to reverse the deficit at Ulster 12 Ospreys 16 on 68 minutes.

Ulster responded manfully, heaping pressure on the Ospreys defence with multiple phases and overlaps, which the visitors resisted with some aplomb until they were able to intercept and clear. With less than five minutes remaining on the clock, an untimely spill from Mike McComish handed possession back to the visitors, who then set about containing Ulster in their own half.

A last-minute Ulster line-out on half-way once again went awry, and although the hosts regained possession through sheer persistence, ball-carrier Lewis Stevenson was soon bundled into touch by a flock of Ospreys to bring the match to an end.

Ulster will have the opportunity to get back to winning ways Friday next, once again at Ravenhill where they welcome Italian outfit Zebre.

Full-Time Score Ulster 12 Ospreys 16

Ulster
(15 - 9) R Andrew; A Trimble, L Marshall, P Wallace, M Allen; S Olding, R Pienaar
(1 - 8) C Black, R Herring, T Court, J Muller (c), L Stevenson, M McComish, A Birch, R Diack
Replacements (16 - 23) N Annett, R Lutton, A Warwick, D Tuohy, N McComb, P Marshall, D Cave, C Cochrane

Ospreys
(15 - 9) R Fussell; T Habberfield, T Isaacs, J Spratt, B John; M Morgan, K Fotuali'i (c)
(1 - 8) R Bevington, S Baldwin, C Griffiths, L Peers, J King, J Bearman, S Lewis, M Allen
Replacements (16 - 23) M Dwyer, D Jones, D Arhip, A-W Jones, A Ellis, R Jones, J Murphy