Neath-Swansea Ospreys survived a late Leinster onslaught to win at Donnybrook and open up a 12-point lead at the top of the Celtic League table.
Leinster (5) 12:
Tries: Warner, Jennings.
Ospreys (3) 16:
Cons: M. Jones.
Pens: Connor 2, M Jones.
The Irish side led 5-3 at the break courtesy of Christian Warner's try.
But Ospreys scrum-half Jason Spice claimed the crucial score on the hour mark, diving over from close range for a converted try.
Leinster hit back when Shane Jennings charged through to set up a thrilling finale, but Ospreys held out to win.
Ireland centre Gordon D'Arcy had his first outing in four weeks after injuring a hamstring in the 28-17 RBS Six Nations win over Italy.
Playing at full-back, D'Arcy sparked some of Leinster's best attacking moves.
But his hamstring appeared to tighten up later in the game and D'Arcy will need careful attention from the Ireland medical staff if he is to face France on Saturday.
The game started in controversial fashion after Spice had what looked a certain try denied by the linesman's flag with five minutes gone.
Replays showed the Ospreys scrum-half had clearly grounded the ball over the try line before his foot brushed the left corner flag.
The visitors did take the lead soon after when Shaun Connor struck a penalty, but the fly-half was wide with two more kickable chances as the Ospreys failed to turn pressure into points.
Leinster gradually began to exert a grip on the game and bossed the possession, but determined Welsh defence held them at bay until just before half-time.
A long pass from fly-half David Holwell found Kieran Lewis and the centre managed to get the ball away in the tackle for Warner to score an unconverted try in the left corner.
Conner's poor kicking form continued after the break with another miss, although he did put the Ospreys back into the lead with a penalty in front of the posts after 57 minutes.
Wales Under-21 fly-half Matthew Jones arrived to take over the No 10 position and added some much-needed spark.
A scrappy but effective series of drives took the Ospreys to the Leinster line and when skipper Barry Williams was tackled just short, Spice was on hand to dive over, Jones converting.
When replacement Leinster prop Emmet Byrne was sin-binned and Jones struck the resulting penalty for a 16-5 lead, it looked all over for Leinster.
But the home side showed great patience and no little skill to carve out a try for flanker Jennings, with Holwell's conversion making it 12-16 with four minutes plus injury time remaining.
Jones missed a penalty that would probably have put the match beyond Leinster, who laid siege to the Welsh line.
Two drives from successive five-metre lineouts were repulsed by the Ospreys, as Leinster ran out of time to find a winning score.
With closest challengers Munster having lost at the Cardiff Blues on Saturday, the Ospreys know that the Celtic League title is now almost within reach.
Leinster: D'Arcy; McWeeney, Warner, McAllister, Lewis; Holwell, Easterby; Lyne, D Blaney, Nebbett, Dillon, Gissing, Potts, Jennings, Costello.
Replacements: G. Hickie, E. Byrne, McCullen, Gleeson, O'Riordan, Norton, Brown.
Ospreys: Terblanche; Tiueti, Bishop, Seveali'i, Mustoe; Connor, Spice; D. Jones, B Williams, Millward, Newman, Bateman, Thomas, Pugh, Bater.
Replacements: R. Hibbard, Griffiths, Tandy, Bonner-Evans, Rees, M. Jones, Durston.
Referee: Andy Ireland (SRU).