RYAN Bevington spurred the Ospreys to victory with a remarkable try that downed the Pro12 leaders at Ravenhill last night.
Steve Tandy's side were ravaged by representative call-ups and injuries and appeared booked for a difficult evening in Belfast.
But they were simply outstanding at Ravenhill, chiselling out a win that will delight the coaches almost as much as any this season.
They had any number of heroes, not least Bevington, Scott Baldwin and Joe Bearman, all of whom worked tirelessly, backed by Cai Griffiths, Morgan Allen, Sam Lewis and James King.
The decisive try came on 66 minutes and it was every bit as special as the performance deserved, a long-range counter attack ending with Bevington storming over from 40 metres.
Ulster threw everything into attack in a desperate bid to save the game. But the visitors' defence held out.
What a victory it was to welcome Alun Wyn Jones back into rugby. He returned on 49 minutes and fittingly made the final tackle.
The Ospreys made the trip to Belfast with a side that wasn't so much weakened as torn apart by international calls and injuries.
They were missing 23 players in all — 16 on duty with Wales at senior and under-20s levels and seven ruled out with various bumps.
But there were still points to be scrapped for, and with the Ospreys having to play six away games in their final nine matches this term, they took the field knowing that hoisting the white flag wasn't an option.
The challenge didn't get much tougher, though.
Ulster were that far in front of the chasing pack a decent pair of binoculars would have come in handy to locate them.
Beaten just once in the league before last night, they had already completed a Grand Slam of victories over the Welsh regions, the sequence including a 48-19 defeat over the Blues in Cardiff, a 46-16 success over the Dragons in Newport and a 47-17 triumph over the Scarlets at Ravenhill.
Ruan Pienaar kicked the Northern Irish province into a 3-0 lead from 32 metres after Sam Lewis had been penalised at a ruck, but Matthew Morgan levelled with a penalty of his own, the wind blowing the ball through the posts after it appeared to be flying wide.
The Ospreys had sent out a press release beforehand alerting the world that three players were featuring in a regional starting line-up for the first time and another two were set for their Pro12 debuts off the bench.
Close on every week it appears to have been the same story: new faces being pitched onto the battlefield.
Accelerated development has been the name of the game and it says much that Steve Tandy's side have managed to stay in contention for a top-four finish.
They trailed 9-6 at half-time last night but had much to be pleased about in the opening 40 minutes.
Morgan missed a drop-goal attempt but he came close to splitting the Ulster defensive line with a darting break from deep minutes later, the fly-half's pass just going to ground.
For all the absentees on both sides, the crowd were at least treated to a contest between arguably the best two scrum-halves in Europe this season, Pienaar and Kahn Fotuali'i.
The Ospreys man had the better of the early stages, using his trademark hanging box kick to good effect and maintaining a high tempo, not least through his ability to think a split-second quicker than anyone else on the pitch.
But Pienaar countered with some wonderful kicking out of hand himself.
Every time the Ospreys gave away a long-distance penalty they looked up and found themselves having to trek back 50 metres.
Ulster had a young fly-half making his first Pro12 start, but any home concerns about Stuart Olding's inexperience would have been eased by the way Pienaar took control of the decision-making. Ulster's game went through their No. 9: they could have had a chimpanzee outside him in the opening half and it wouldn't have mattered.
Nonetheless, Bearman, Allen, Baldwin, Bevington and James King kept the hosts honest with powerful ball-carrying in the opening half-hour, the battery of big forwards trucking the ball up and invariably crashing over the gain-line.
At one point the visitors took the ball through 15 phases but were unable to convert the pressure into points, Richard Fussell running out of options and forced to kick the ball away.
But the Ospreys kept on the offensive. They piled on the pressure at the scrum, with Bevington giving Tom Court an outing, and showed adventure with ball in hand.
Yet they were behind at the break after Pienaar completed a penalty hat-trick, with Morgan firing over a second penalty shot himself for the Welsh side.
It came back to execution.
You can have all the possession in the world but the key is translating it into scores on the board.
Alun Wyn Jones came on in the 49th minute, just in time to see Morgan level the scores at 9-9 with a well-struck penalty.
But Ulster suffered a blow soon after when Pienaar left the field with a suspected rib injury.
They nonetheless mounted a ferocious offensive that culminated in a penalty that Olding converted. The Italian referee threw salt in by showing Allen a yellow card for a ruck offence that was debatable at best.
Trailing 12-9, the Ospreys roared into the lead with one of the tries of the season, Jonathan Spratt breaking from deep down the touchline and finding Fotuali'i in support.
Showing huge composure, the scrum-half flighted the ball inside to Bevington.
The prop had 40 or so metres still to cover but he put his foot on the accelerator to crown a devastating counter, Morgan's conversion making it 16-12 to the region.
But the 14-man visitors were forced into desperate defence in which virtually every player put in tackles.
It was a game that defied expectations and it also kept the Ospreys on course for a top-four finish and a placed in the play-offs.
"The boys were brilliant," summed up assistant coach Jonathan Humphreys.