Dan Biggar kicked two penalties for Ospreys giving his side a marginal lead going in at the break, 6-3 to Ospreys at halftime.
The boot of Biggar continued to drive Ospreys ahead as he kicked a further 3 penalties in the second half.
Munster responded with an O'Gara penalty and a try on the 70th minute, but missed opportunities were to the detriment of Munster and in the end they had to contend with a losing bonus point.
Munster 11 Ospreys 15.
A disappointed Tony McGahan afterwards "We were well beaten in the end, they competed on every ruck, and every ball we did have was really slow and they put alot of pressure on us and they won turnover ball."
"It was a big game for us today and we needed a result. I know we showed a little fight to come back in the game but it wasn't enough at that stage."
When asked how Munster will look to bounce back from the loss, McGahan replied "We have shown it already this year if we have a disappointing result we can certainly come back from it, and we will re-group this week and next weekend is what this year is all about for us and we're chasing a Heineken Cup."
And an update on the injury front "We're very hopeful with Ian Dowling, Doug Howlett and Keith Earls, and Paul O'Connell is in a race against time at the moment so we're just giving them every opportunity at this point and we will look at everyone's progress during the week."
Jean de Villiers on his last game in Thomond Park "It definitely wasn't the way I wanted to finish it off, but it's not the fact that it's my last game, it's more that we didn't play is why I'm so disappointed."
"Ospreys were just more clinical today and our discipline wasn't the best tonight. Opportunities were created but we just didn't finish them off and they were just the better team on the day."
"We certainly have to step it up for next week. It's make or break now and it's the time of the season where we have to win every game."