A determined final quarter comeback saw Ulster inflict a second successive defeat on defending RaboDirect Pro12 champions the Ospreys at the Liberty Stadium with replacement Paul Marshall grabbing the crucial score five minutes from time.

It means the Welsh region have now slipped to two losses in their first two matches of the season having lost to Benetton Treviso in their opening fixture. They appeared well set to take the win after Hanno Dirksen's converted try and two penalties from Matthew Morgan meant they had the lead with 10 minutes to go.

All Ulster had to show by then were three penalties - one from Niall O'Connor and two from Jackson, but Jackson's try turned the match on its head and the Ospreys were unable to respond in the final minutes.

The Ospreys had enjoyed the better of an error-strewn first half, lit up by a moment of brilliance from South African-born speedster Dirksen. There was plenty of intent shown from both sides, but all too often promising attacks were undone by sloppy handling and it took until 22 minutes for the game to come alive when right wing Dirksen produced a superb individual run to claim the game's first try.

He picked up a loose pass 35 metres out and hurtled through a fragile defence, fended off Ulster full-back Jared Payne and then sped away to reach the line unopposed. Morgan added the extras, but the Ospreys failed to build on their lead as mistakes continued to plague their game.

Fly-half Niall O'Connor made up for an earlier miss to land a long-range penalty after 31 minutes, but he failed with an ambitious attempt from inside his own half just before the break as the Ospreys went in at half-time 7-3 ahead.

Two penalties from Morgan after the break extended the home side's advantage as the champions attempted to assert control, but a clutch of substitutions by Ulster coach Mark Anscombe turned the match on its head. The arrival of props John Afoa and Tom Court reinforced the Ulster scrum, while Stephen Ferris produced some thunderous tackles.

Another replacement, Jackson, landed two penalties to make it 13-9 before replacement scrum-half Marshall, claimed the match-winning score with six minutes remaining. A sharp counter-attack from wing Craig Gilroy set up the opportunity which eventually allowed Marshall touch down from close range. It needed the television match official to confirm the score, but Marshall and his Ulster team-mates were in little doubt.

It left the Ospreys with little time to redeem themselves, but any chance they had of salvaging the win disappeared when they coughed up the ball again. The loss leaves them with just two losing bonus points to show from their opening two matches.