Leinster wing Andy Conway scored the first try but was injured later
Ospreys inched ahead of Leinster to take fifth in the Magners League table with a hard-fought win in Swansea.
The Irish visitors led 10-9 at half-time thanks to a try from wing Andrew Conway, who was later carried off with a worrying neck injury.
Dan Biggar's fourth penalty edged Ospreys in front but Isa Nacewa restored Leinster's lead with a try.
But a penalty try from a scrum gave Ospreys the win while Leinster had Ian Madigan and Ed O'Donoghue sin-binned.
Barry Davies; Gareth Owen, Sonny Parker, Ashley Beck, Richard Fussell; Dan Biggar, Rhys Webb; Duncan Jones, Richard Hibbard, Craig Mitchell, Ian Gough, Ian Evans, Justin Tipuric, Marty Holah, Jerry Collins (capt). Replacements: Mefin Davies, Joe Rees, Cai Griffiths for Justin Tipuric (23-29), James Goode for Ian Evans (66), Tom Smith for Collins (66), Jamie Nutbrown for Rhys Webb (48), Matthew Morgan, Tom Isaacs for Barry Davies (48).
Leinster: Isa Nacewa; Shane Horgan, Eoin O'Malley, Fergus McFadden, Andrew Conway; Ian Madigan, Isaac Boss; Heinke van der Merwe, Jason Harris-Wright, Clint Newland, Leo Cullen (capt), Ed O'Donoghue, Dominic Ryan, Shane Jennings, Stephen Keogh. Replacements: Tom Sexton, Mike Ross for Clint Newland (41), Jack McGrath, Eoin Sheriff, Rhys Ruddock for Dominic Ryan (60), Paul O'Donohoe, Ian McKinley, Dave Kearney for Andrew Conway (48).
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