Leinster lost this battle of the Celtic heavyweights as the Ospreys handed them a three-try defeat in a lively RaboDirect PRO12 opener in Swansea.
Captained by Rhys Ruddock and wearing their all white away strip, Leinster struggled for continuity in the first half and were 17-0 down inside the opening 20 minutes.
The Ospreys used an early turnover to set up influential scrum half Rhys Webb for the opening try after just 93 seconds.
They countered down the right and although there was a hint of a forward pass, play continued and Andrew Bishop offloaded for Webb to score in the corner.
Dan Biggar swung over the conversion from the right. Starved of territory, Leinster did well to clear their lines through young debutant scrum half John Cooney as the hosts continued to dictate.
Ruddock was unfortunate to concede a penalty for hands in the ruck which allowed Biggar stretch the lead to 10-0. New signings Mat Berquist and Damian Browne made their presence felt as Leinster’s general play improved.
Ruddock and Jamie Hagan combined to hold up Jonathan Thomas as the Ospreys hunted for their second try. However, the Welsh region got over just moments later, with Hanno Dirksen sliding over past David Kearney’s tackle in the corner.
Berquist missed a long range penalty from the left and despite some encouraging runs from Dominic Ryan and Isa Nacewa, the Ospreys kept the scoreboard ticking over thanks to a Biggar drop goal.
Berquist kicked Leinster’s opening points in the 31st minute, slotting a penalty from the 22 after strong carries from Heinke van der Merwe and Kevin McLaughlin.
The action was much more competitive in the lead up to half-time, with Kearney, Luke Fitzgerald and the hard-hitting McLaughlin coming more into the game.
Leinster were pressing for a late score when the Ospreys hacked downfield. Suddenly, another frustrating turnover opened the door for Webb to chip over the top, and stand-in skipper Justin Tipuric raced onto the ball for try number three.
Biggar’s conversion made it 27-3 at the break. Leinster went close to responding in the opening minutes of the second half. A knock on spoilt a promising move, following a Berquist touchfinder and a solid lineout maul.
Joe Schmidt’s men continued to batter away at the Ospreys defence. A television match official decision went against the hard-working McLaughlin who had barrelled his way over the line.
Tipuric was banished to the sin-bin after repeated infringements by the Ospreys at the breakdown, yet Leinster could not make use of the extra man.
In the final quarter, the busy Fionn Carr was called back for a forward pass as he threatened to break the try deadlock for the province.
Leinster were clearly missing the influence of the 14 players away on Rugby World Cup duty, but the youngsters, including replacements Jack McGrath and Brendan Macken, gained valuable experience in a closely-fought second period.
The Ospreys threatened to score a bonus point try in the closing stages, however this youthful Leinster side were on their guard and will take some positives into next weekend’s visit of the Dragons to the RDS.
OSPREYS SCORERS: Rhys Webb (1 try), Hanno Dirksen (1 try), Justin Tipuric (1 try), Dan Biggar (3 conversions, 1 penalty, 1 drop goal)
LEINSTER SCORERS: Mat Berquist (1 penalty)
OSPREYS: R Fussell; K Phillips, A Bishop, A Beck, H Dirksen; D Biggar, R Webb; D Jones, M Davies, C Griffiths, I Gough, I Evans, T Smith, J Tipuric CAPTAIN, J Thomas.
REPLACEMENTS: M Dwyer, K Dowding, J Rees, J King, M Allen, T Isaacs, M Morgan, S Parker.
15: Isa Nacewa
14: Fionn Carr
13: Eoin O’Malley
12: Luke Fitzgerald (Brendan Macken, 57)
11: David Kearney
10: Mat Berquist (Ian Madigan, 52)
9: John Cooney (Cillian Willis, half-time)
1: Heinke van der Merwe (Jack O’Connell, 77)
2: Richardt Strauss (Aaron Dundon, 68)
3: Jamie Hagan (Jack McGrath, 57)
4: Damian Browne (Mark Flanagan, 57)
5: Devin Toner
6: Kevin McLaughlin
7: Dominic Ryan
8: Rhys Ruddock CAPTAIN (Leo Auva’a, 62)
REFEREE: Peter Fitzgibbon (IRFU), ASSISTANT REFEREES: Gwyn Morris, Jon Mason (both WRU), TMO: Neill Ballard (WRU)