The Ospreys returned into the home semi-final spots on Saturday courtesy of a hard-fought 15-11 victory over Munster at Thomond Park.
Dan Biggar's right boot did all the damage as the Welsh claimed their first ever win at the Limerick venue, moving themselves a step closer to a home Magners League semi-final.
Biggar kicked five penalties from five attempts as the Ospreys moved back into second place in the league table, with just one round of games to go.
Munster's stand-in captain Ronan O'Gara scored a try and kicked two penalties but he also missed four other kicks, totalling 11 points, as the Irish side's hopes of defending the league title took a serious hit.
The result leaves Munster in fourth place in the standings, meaning they will have to beat the Cardiff Blues away in two weeks' time and hope that other sides slip up in order to reach the semi-finals.
In damp conditions, there was no real pattern in the opening half, and both sides struggled to gain a foothold amid dropped passes, aimless kicks and a general lack of urgency.
Munster played most of the attacking rugby and they enjoyed a large chunk of territory while failing to trouble the try-line.
Flanker David Wallace put in some big carries to spark some much-needed life into the game, one of which saw him set up winger Scott Deasy for a darting run into the 22.
But the Ospreys, with Ryan Jones and Marty Holah tackling effectively, were able to soak up the pressure and O'Gara's 11th-minute penalty was the only score of a flat first quarter.
He missed two further penalty chances, the second of which was particularly kickable, and his opposite number Biggar was bang on target with his two opening efforts after 23 and 31 minutes.
Prop Paul James foraged well at a ruck to tee up the young outside-half for a smashing strike from distance, and he punished Alan Quinlan with another well-struck effort on the half hour, setting up a 6-3 half-time lead.
Paul Warwick got closest to breaching the try-line but his sniping run on the left was ended by a knock on, forced by a Jerry Collins tackle.
The Ospreys seized the initiative at the start of the second half with a Wallace offside allowing Biggar split the posts again, and Munster had to scramble back to deny Andrew Bishop a try after a Mike Phillips break.
Two more successful kicks from Biggar, the second coming after Munster number eight James Coughlan was sin-binned for hands in the ruck, left the home side with a mountain to climb at 15-3 down.
Munster cranked it up for the final quarter, with O'Gara kicking his second penalty, but worryingly, with their Heineken Cup semi-final trip to San Sebastian looming next week, they were never able to hit top gear.
A lovely counter-attack from Lifeimi Mafi and Deasy got them within scoring range and Ospreys skipper Ryan Jones was sin-binned at the next phase for illegally collapsing a maul.
Holah held up replacement hooker Damien Varley as the Munster pack tried to sniff out a try, which arrived on 71 minutes when Deasy sniped through, setting up a ruck from which O'Gara attacked the blindside and got over.
But he could not add the conversion from wide out on the right and the Ospreys, with Tommy Bowe and Jerry Collins putting in some telling hits, deservedly held on to become the first Welsh region to win in Limerick since the Dragons did so six years ago.
Pen: O'Gara 2
For the Ospreys:
Pen: Biggar 5
Munster: 15 Paul Warwick, 14 Tom Gleeson, 13 Lifeimi Mafi, 12 Jean De Villiers, 11 Scott Deasy, 10 Ronan O'Gara (c),9 Tomas O'Leary, 8 James Coughlan. 7 David Wallace, 6 Alan Quinlan, 5 Mick O'Driscoll, 4 Donncha O'Callaghan, 3 John Hayes; 2 Jerry Flannery, 1 Marcus Horan.
Replacements:16 Damien Varley, 17 Julien Brugnaut, 18 Billy Holland, 19 Niall Ronan, 20 Peter Stringer, 21 Denis Hurley, 22 Simon Zebo.
Ospreys: 15 Lee Byrne, 14 Tommy Bowe, 13 Andrew Bishop, 12 James Hook, 11 Shane Williams, 10 Dan Biggar, 9 Mike Phillips, 8 Ryan Jones (c), 7 Marty Holah, 6 Jerry Collins, 5 Jonathan Thomas, 4 Ian Gough, 3 Adam Jones, 2 Huw Bennett, 1 Paul James.
Replacements: 16 Ed Shervington, 17 Ryan Bevington, 18 Alun Wyn Jones, 19 Filo Tiatia, 20 Jamie Nutbrown, 21 Sonny Parker, 22 Nikki Walker.
Referee: Neil Paterson