Munster lost their six year unbeaten run against Welsh opposition at Thomond Park as they went down to a 15-11 defeat to the Ospreys in a crucial Magners League match.
The Heineken Cup semi-finalists worked their way back to within four points and ended the game hammering away at the Ospreys line, but just came up short.
For the Ospreys, who bowed out of the Heineken Cup against Munster's semi-final opponents Biarritz Olympique by a single point at the quarter-final stage, it was small revenge for their last eight mauling in Europe last season at the same venue.
Munster skipper Paul O'Connell once again sat out the game, as did fellow British & Irish Lion Keith Earls and first-choice wings Doug Howlett and Ian Dowling.
With a home draw in the Magners League semi-finals at stake this game between the second and third placed teams had extra edge and the home side came up with the only try of the game.
It fell to skipper on the night Ronan O'Gara - his first of the season - and brought Munster back to within four points of their rivals. But while O'Gara picked up all the points for his side, he also uncharacteristically missed with two penalties in the first-half and the conversion of his own try in the second.
By contrast, opposite number Dan Biggar hit the mark with five penalties to steer his side to victory - and to within a home win over the Dragons in two weeks time of possibly clinching a home semi-final.
Those two O'Gara penalty misses in the opening period allowed the Ospreys to weather the storm and go into the break with a 6-3 lead. Biggar extended that advantage to 15-6 before Munster No 8 James Coughlan was sent to the sin-bin.
It took some magnificent defending from the home side to keep the Ospreys at bay while they were a man down, but they did manage to close the gap with a second O'Gara penalty.
Ospreys skipper Ryan Jones then got his marching orders for 10 minutes for collapsing a driving line-out maul and O'Gara flashed around the narrow side of a close range ruck to score a try that brought his side back to within a score of winning.
But the Ospreys held out to make it a notable Magners League double over their Irish rivals and steal a march in the race for a home semi-final. Defeat for Munster means they will have to go to Cardiff Blues the week after their Heineken Cup semi-final in San Sebastian and win to be sure of a place in the Play-Offs.
