The Ospreys won the first-ever Magners League Grand Final by beating Leinster at the RDS in Dublin on Saturday night.
Tommy Bowe raced over for the Ospreys' first try in the 19th minute, with Dan Biggar converting to make it 7-0.
Jonathan Sexton kicked a penalty but Lee Byrne added the second try before half-time, Biggar again adding the two points to increase his side's lead.
Sexton was successful with three of his four second-half penalty attempts, with Biggar kicking a penalty for Ospreys.
The match was the last in charge for Leinster head coach Michael Cheika and both sides were aiming to win the Magners League for a record third time.
Leinster had been crowned champions in 2002 and 2008 while Ospreys had won the Celtic title in 2005 and 2007.
Leinster had finished top of the table, with Ospreys second, but it was the Welsh side who lifted the trophy thanks to their first-ever victory at the Dublin ground.
Biggar crossed the home side's line after two minutes but referee Chris White had already blown up for a forward pass.
Jones takes a Magners shower
The Ospreys fly-half missed with a relatively straightforward penalty attempt in the 14th minute but then played a significant part in his side's opening try five minutes later.
Biggar offloaded to Andrew Bishop, who broke away, cut inside Gordon D'Arcy and passed to Bowe, who raced over the line to touch down for his eighth try of this season's Magners League campaign.
Biggar made amends for his earlier miss by adding the conversion to make it 7-0.
The Irish province replied with their first points of the game, a Sexton penalty after 22 minutes.
Ospreys enjoyed the majority of territory and possession and should have scored their second try when Jerry Collins bore down on the line but a misplaced pass saw the opportunity pass.
Irish internationals Shane Horgan and Rob Kearney made breaks out of their own half but both were halted by strong tackles.
The Ospreys did manage to cross the Leinster line for the second time in the 34th minute, courtesy of a fine passing move among the backs which carved open their opponents' defence.
James Hook passed to full-back Byrne who showed an electric burst of pace to evade an attempted tackle by Jamie Heaslip and score in the corner.
Shane Jennings gets to grips with Ryan Jones at the RDS
Biggar was again on target with the conversion to give his side a 14-3 lead at the interval.
Sexton reduced his side's deficit with a long-range penalty four minutes into the second half following an infringement by Alun Wyn Jones.
Biggar restored the Ospreys' 11-point advantage by knocking over a simple penalty three minutes later and could have added a drop-goal soon after but the fly-half chose to pass to Hook, who badly miscued his attempt.
Leinster then piled on the pressure but were held up just short of the line.
Ospreys were forced to concede a penalty which Sexton converted from in front of the posts to maintain his 100 per cent record with the boot.
The Irish fly-half kicked a further penalty with 10 minutes remaining after Byrne was penalised for a high tackle on D'Arcy, but missed with another effort three minutes from time.
Leinster: Rob Kearney; Shane Horgan; Brian O'Driscoll, Gordon D'Arcy; Isa Nacewa; Jonathan Sexton, Eoin Reddan; Stan Wright, John Fogarty, CJ van der Linde, Nathan Hines, Malcolm O'Kelly, Kevin McLaughlin, Shane Jennings (capt), Jamie Heaslip Replacements: Richardt Strauss for Jennings (67), Cian Healy for van der Linde (48), Trevor Hogan for S Keogh (42), Stephen Keogh for McLaughlin (30), Paul O'Donohoe, Fergus McFadden, Girvan Dempsey
Ospreys: Lee Byrne; Tommy Bowe, Andrew Bishop, James Hook; Shane Williams; Dan Biggar, Mike Phillips; Paul James, Huw Bennett, Adam Jones, Alun Wyn Jones, Jonathan Thomas, Jerry Collins, Marty Holah, Ryan Jones (capt) Replacements: Ed Shervington, Ryan Bevington, Ian Gough for J Thomas (62), Filo Tiatia for R Jones (67), Jamie Nutbrown, Gareth Owen, Nikki Walker for Williams (71)
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