Ulster went into the match fully aware of their somewhat lacklustre recent record against the Swansea-based outfit, with only two victories in the sides' last six encounters.

However, a penalty try and a quality team try finished off by Paddy Wallace made the difference, elevating Ulster up to fourth place in the standings with six rounds remaining.

With an Ulster scrum on the Ospreys' ten-metre line eventually successful at the third time of asking, the hosts put a series of good passes together and unleashed Nevin Spence into the 22.

The Ospreys defence braced itself and used its numbers to withstand the powerful centre first on the left flank, then moments later on the right, and subsequently turned possession over and managed to clear.

An Ospreys offside in the very next passage of play, however, gave Ruan Pienaar to go for the posts from distance, but his kick dropped marginally wide.

The Ospreys looked slick and well drilled as they mounted their first attack on the quarter hour, and with Pedrie Wannenburg sin-binned for blocking and failing to retreat at the concession of a penalty, his opposite number Joe Bearman capitalised on the advantage to ground a try after good lineout work from the Ospreys.

Dan Biggar added the extras and then the game cranked up a gear, with a strong Ulster rolling maul gaining a good 20 metres before excellent play from both Paul Marshall and Spence got the home side back into the danger zone.

The attack was blighted by referee Neil Hennessy's call for a forward pass, but Ulster soon had some recompense for their travails, courtesy of a sweetly-struck Pienaar penalty on the half hour mark.

Another chance was not long in coming, with Marshall, Wallace and Wannenburg all linking up effectively on the left wing 90 seconds later to force a second penalty.

Pienaar's kick dropped inches short of the crossbar, but an undeterred Ulster came at the Ospreys again, collecting the clearance and bursting menacingly down the left wing. The try-scoring opportunity was only scuppered when Ian Whitten's final pass in-field somehow fell into a pair of Welsh hands.

Again the Ospreys cleared their lines, and once more Ulster thrust upfield without delay. This time their persistence paid off.

After several phases of play and even a Marshall-style 'tap and go' from Wannenburg, the desperate Ospreys defence infringed once too often for Hennessy's liking, and he awarded a penalty try.

An intentional knock on of a final pass just shy of the try-line by Biggar was the straw that broke the camel's back, and the out-half's intervention saw him yellow carded for good measure. Pienaar converted to cement a 10-7 interval lead.

Despite their numerical disadvantage in Biggar's absence, the Ospreys started the second half with the greater attacking intent.

But once Ulster had contained five minutes' worth of threat, a turnover in midfield allowed them to make their superiority count. Good pressure and recycling down the right flank got Ulster well inside the Welsh side's 22.

With bodies lining up on the overlap on the left wing, swift cross-field passing allowed Whitten to supply Wallace for a dive in at the corner. The angle was too tight for Pienaar's conversion, but the lead was promising at 15-7.

The Ulstermen's next onslaught saw Lewis Stevenson and Dan Tuohy do all the groundwork, grinding out the yards and creating the space for John Afoa to propel his way through, halted only by a stubborn Welsh grip on his jersey.

The Ospreys managed to win turnover ball at the next phase, but with Ulster dominating now a third try at this stage seemed a formality.

The Ospreys had other ideas, however, and refused to be swept away by the white and red tide, completely reversing the run of play in the last quarter hour.

The first to show was right winger Hanno Dirksen, whose 66th minute dash saw him evade several tackles before Stefan Terblanche snuffed oute the danger in timely fashion.

With Brian McLaughlin ringing multiple personnel changes in the closing 10 minutes, Ulster's task was now all about containing the resurgent Ospreys.

They held out until the 79th minute when winger Eli Walker was adjudged to have touched down just over the try-line after an impressive solo raid in-field.

Biggar's conversion closed the gap to a solitary point, and Ulster hearts were in their mouths when the Ospreys burst down the right wing in the dying seconds, the speedy Dirksen instrumental again.

With the clock at 80 minutes, Biggar kicked cross-field into the left hand corner where several recipients were waiting, but fortune smiled on Ulster as the ball landed in Afoa's arms, and the prop gratefully punted into touch to signal the end of the game.