Edinburgh took their losing streak into double figures and will also be without Scotland centre Nick De Luca for a lengthy period after he was sent off in the closing minutes of an unimpressive encounter.
Scorers: Ospreys: Tries – Allan (2), Webb. Cons – Morgan (3). Pens – Morgan. Edinburgh: Try – Watson. Con – Leonard.
He saw red for a tip tackle on Ospreys replacement wing Tom Graham. It was one of those slightly unlucky tackles where the player with the ball comes down at a bad angle, however De Luca did pick him up in the air without being able to correct the momentum of the hit. A player of his experience should know better and that summed things up for Edinburgh on a bitterly cold night in South Wales.
They did manage to prevent the Ospreys claiming a bonus point as the defending champions pursue a place in the top four this season, but that was little consolation for Edinburgh in a losing streak which stretches back to the start of December.
They need something to break the downward spiral, it is only the poor form of the Dragons and Zebre, who face each other this weekend, which is keeping the Scottish side from the bottom of the table.
Edinburgh had a young side out, missing all their internationals of course, although the Ospreys were in the same position and had more players under the age of 23 than the Scots.
Edinburgh were also trying to end a nine-match losing run and they did not get the best of starts as the Ospreys got their first try after just five minutes, several waves of forward attacks eventually bringing a reward with No 8 Morgen Allen going over for the try, converted by Matthew Morgan.
It was a formula which worked so well, that a few minutes later they repeated it, Allen going over from close range once again and Morgan adding the conversion. In between that Harry Leonard had a relatively simple penalty attempt, but put it narrowly wide as Edinburgh had a good period of pressure without getting on the scoreboard.
Coming up to half-time it looked as though the only question was going to be whether the home side would romp to an early bonus point, when Edinburgh threw themselves a lifeline. It started from inside their own half with a loose kick being taken by wing Dougie Fife, who handed on to No 8 Netani Talei who took the ball forward before handing back to Fife to take the ball up to the Ospreys right-hand corner.
The ball was spread wide where openside flanker Hamish Watson, enjoying his first start, showed good pace to use the players outside to draw the defence as he went over for the try. Leonard converted from wide out.
The second half started with plenty more Ospreys possession and pressure, but the turning point came after around a quarter of an hour after Edinburgh captain Sean Cox had been warned that his players were lying offside too much for the liking of Irish referee David Wilkinson.
With the general warning having been issued the next offender was going to visit the sin-bin. Centre Ben Atiga was unfortunate to be that man, but Edinburgh going down to 14 men was pivotal.
The Ospreys stepped up the pressure and scrum-half Rhys Webb went over for the try in the corner after full-back Richard Fussell had made the ground with a clean break. The Ospreys had scored three tries with a total of three yards carried to bring them. Morgan added the conversion to go with a second-half penalty as the Ospreys started pursuing the bonus point with the win in the bag.
They made too many mistakes and the Edinburgh defence was able to hold firm, but the Scots were unable to sustain any pressure of their own. The breakdown was a particular area of weakness, the home side found it too easy to steal possession in that area.
This was summed up when scrum-half Webb was able to rip the ball from the grasp of prop Allan Jacobsen.
He went 60 yards upfield before the defence got across to snuff out the move. It was more bad news for Edinburgh when De Luca was sent off for the tip tackle on Ospreys replacement Tom Grabham.
Edinburgh survived conceding the fourth try by hook or by crook, but they have bigger problems facing them as they try to end this losing streak.
Ospreys: R Fussell; T Habberfield T Isaacs, J Spratt K Fotuali’I (Capt); M Morgan, R Webb R Bevington S Baldwin C Griffiths L Peers J Thomas, J King S Lewis, M Allen. Subs: M Dwyer , M Thomas, D Arhip for Griffiths 63 , S Williams, D Baker for Allan 78 , A Ellis for Lewis 62, A Beck for Spratt 52, T Grabham for Habberfield 72.
Edinburgh: G Tonks; D Fife, N De Luca, B Atiga, L Jones, B Cairns 23); H Leonard, R Rees, J Yapp, A Titterell, W Nel, P Parker, S Cox (Capt), S McInally, H Watson, N Talei. Subs: R Hislop , A Jacobsen for Yapp 54, A Allan for Nel 67, R McAlpine for Parker 67, C Leck for Rees68 , P Francis, T Brown for Tonks 5 – 17 and for L Jones 20-23, B Cairns for Brown 23.