The Ospreys coughed up a seven-point interval lead as Leinster scrum-half Brian O’Meara matched Gavin Henson kick for kick, and the sides shared two tries.
The Ospreys took the lead in the 12th minute as inside centre Dave Tiueti cut loose and looped well for international Shane Williams to run over, completing a 30-metre drive.
Williams’ fourth of the season was converted by Henson, before Leinster enjoyed their first bout of pressure.
The Welsh outfit were to go scoreless until the second minute of first half injury time as Henson brought about Malcolm Changleng’s half-time whistle with a left-sided 25-metre penalty.
Leinster’s only score in a 10-3 half-time deficit came on 18 minutes when Gordon D’Arcy, back at centre to cover for Brian O’Driscoll’s absence with fellow international Shane Horgan on his right shoulder, was impeded.
O’Meara kicked the resulting straight effort from 25 metres out to go 7-3 up.
The wind curled O’Meara’s second kick wide on 26 minutes, but the game turned on its head just two minutes into the second half.
A high challenge by prop Duncan Jones on D’Arcy saw the Irish centre forced off with injury and loose head Jones sin-binned by Changleng.
O’Meara kicked the penalty and added the extras to a Horgan-inspired try from full-back Jimmy Norton on 47 minutes as Leinster moved their tally to 13.
Henson levelled matters just past the hour as he claimed his 299th point of the campaign with his second penalty.
The Neath full-back exchanged penalties with O’Meara on 69 and 73 minutes.
Leinster number eight Victor Costello, in his 100th provincial appearance, did well to block Henson’s drop goal attempt with two minutes remaining.