Warm-up defeats in Toulon and against the English champions, Wasps had not caused the Ospreys coach, Lyn Jones, any sleepless nights, he said, and he continued to pursue his investment in youth.
In contrast to the English clubs' problems over player availability the Ospreys rested four Lions and two of last season's Grand Slam winning Wales side joined them on the sidelines.
A youthful team showed no signs of missing them as the centre Andrew Bishop provided the first try of the season after only 20 seconds. He charged down Rob Kearney's attempted clearance.
Matthew Jones popped over the simple conversion and did the same 20 minutes later when the captain, Barry Williams, completed a five metre line-out drive with the second home try.
The Ospreys launched last season with a home win over Munster, and Leinster looked like going the same way. But three penalties from the captain, Felipe Contepomi, two in the last minute of the half, gave the Irish side some hope.
Those hopes rose even higher when Brendan Burke almost collected his own kick in the home 22 with the line begging and Contepomi landed his third penalty in five minutes to cut the deficit to two points. Leinster's cause was also helped when Lyndon Bateman was sent to the sin-bin for the offence that allowed Contepomi to make it three from three.
They were relieved, however, when Jones missed with a third kickable penalty from 40 metres, even if it did come back off an upright and force Kearney to concede a defensive scrum.
Leinster survived that scare, but they had no answer to Jason Spice's runaround move that created an overlap for Bishop to notch his second try eight minutes from time.
Girvan Dempsey inspired a Leinster breakout which paved the way for Kearney to cross wide on the left and cut the gap to two points. Contepomi was narrowly wide with his conversion but made no mistake when he was gifted a penalty shot in front of the posts a minute from time when Steve Tandy was caught offside.
Ospreys: Tries A Bishop 2, B Williams; Conversion M Jones 2; Penalty M Jones. Leinster: Try Kearney; Penalties Contepomi 5.
Ospreys: S Terblanche; R Mustoe, S Parker, A Bishop, A Brew (L Davies, 48); M Jones, J Spice (R Wells, 80); D Jones (Millward, 67), B Williams (capt; H Bennett, 67), A Millward (P James, 34-41; 56), A Newman, L Bateman, L Beech (A Jones, 78), S Tandy (A Jones 40-41), A Lloyd (A Jones, 10-20).
Leinster: G Dempsey; R Kearney, K Lewis, F Contepomi (capt) B Burke; C Warner, B O'Meara (G Easterby, 58); R McCormack (E Byrne, 67), B Jackman (D Blaney, 77), W Green, D Dillon (S Crawford, 61), B Gissing, C Potts, K Gleeson, E Miller (J Heaslip, 45).
Referee: R Pickson (Scotland).Reuse content