It was a victory that leaves the Swansea outfit two points clear of Leinster but crucially they have a game in hand. However, first of those is away to a Glasgow Warriors side who tonight defeated Ulster in Ravenhill and then they have to go to Rodney Parade. So they still have an awful lot to do if are to snatch the title from the leaders.
Leinster had opportunities early on off turnover ball before Shaun Connor's kick from his 22 to the other, and then break almost reaped dividends as the Ospreys brought play close to the Leinster line. After what had been an enterprising start by both sides the crowd were then treated to a bout of kicking more suited to Croke Park.
We might have had the opening score in the 18th minute when Felipe Contepomi was penalised for not releasing after being wrapped by Ryan Jones, but Connor's was wide from a kickable position. For all their possession Ospreys were easily contained although they did open the scoring with a Connor's penalty in the 24th minute after Leinster had killed the ball as Ospreys threatened.
Contepomi leveled from 45 metres four minutes later but Justin Marshall scored the game's opening try in the 31st minute and only a marvellous Gordon D'Arcy tackle prevented Connor's adding to that score.
Then in injury time Shane Horgan picked off a woeful Marshall pass - and not the first dreadful one he threw in this half - to race in for a soft though not undeserved score to level the scores level (10-10) at half-time.
Two minutes into the restart Luke Fitzgerald showed his worth with a break that took Leinster to five metres from the Ospreys line only for them to be penalised for a crooked feed to their own scrum.
Leinster took the lead with a piece of brilliance from Contepomi whose try was created when Robert Kearney collected his own imperfect 'up and under'. Contepomi added the extras for a seven point lead (10-17).
There followed a delightful chip n chase from Girvan Dempsey as Leinster started to take control before Ospreys introduced James Hook in the 51st minute. His first serious contribution came in the 57th minute when he landed a 45 metre penalty to leave four points separating the sides (13-17) and with fourteen mnutes to go he was on the mark again to leave just one point separating the sides.
From the restart and a good claim by Leinster, Jamie Heaslip knocked on, handing possession to the Ospreys and moments later the Leinster number 8 was yellow carded for a professional foul but Hook was wide with his penalty from half-way.
However, Horgan was quite rightly penalised for obstruction in the 74th minute and Hook kicked Ospreys into a narrow lead that they clung onto till the end.