Leinster withstood a sustained final-quarter onslaught from Harlequins to claim a 6-5 victory at The Stoop on Sunday, thus setting up a mouth-watering an All-Ireland Heineken Cup showdown with Munster at Croke Park next month.
Michael Cheika’s men have long been vaunted for their attacking prowess but it was their defensive excellence which shone through in an absorbing last eight encounter in which they were forced to long play long periods under siege inside their own half.
Two penalties from Felipe Contepomi had helped them into a six-point advantage at the break, but Harlequins’s incessant second-half pressure looked set to be rewarded when Chris Brown crashed over on 65 minutes.
However, Chris Malone, on as replacement for the injured Nick Evans, missed the subsequent conversion attempt to leave Quins trailing by a point.
Malone then limped off injured and Brown, who had been entrusted with the goal-kicking responsibilities as a consequence, then squandered a penalty attempt on 75 minutes before a hobbling Evans, reintroduced as a blood replacement for Tom Williams, failed with a last-gasp drop goal attempt.
The game may have yielded only three scores but it was utterly absorbing from start to finish.
Defensively, both sides were excellent and Leinster were particularly impenetrable.
They should have fallen behind seven minutes when an awesome hit from Jordan Turner-Hall - who was impressive throughout - on Felipe Contepomi eventually forced the Argentine into being penalized for holding on.
The resulting kick on goal was from a central position and no more than 30 meters out, but Evans inexplicably pulled his kick to the left.
Just over ten minutes later, Contepomi confidently stroked Leinster into the lead after James Percival had been deemed guilty of not rolling away.
That temporarily settled Leinster and they enjoyed a brief period of dominance.
However, for the most part, they were struggling. Their kicking game was particularly poor, with their star duo Contepomi and O’Driscoll the most culpable in this regard.
Harlequins slowly took control of the game and looked menacing every single time Turner-Hall took the ball up the middle.
They had several half-openings in the second quarter but, crucially, they did not take one.
It was hard to be too critical of them in that regard, though, because Leinster were
Quins looked certain to score on the half hour when Ugo Monye received possession wide on the left, but the combined efforts of Chris Whitaker and Gordon D’Arcy resulted in a magnificent turnover for Leinster.
If that episode frustrated Quins, what unfolded just before the interval must have left them utterly bewildered.
O’Driscoll, who did his chances of earning the Lions captaincy no harm at all with another inspirational display, picked up possession in midfield and cleverly lobbed the ball in behind the Quins back-line. The ball bounced up beautifully into O’Driscoll’s path and he raced away towards the line.
David Strettle and Monye managed to catch the Ireland centre but O’Driscoll still managed to recycle the ball for Whitaker.
However, as the Aussie scrum-half attempted to pass it wide, Easter got in the way, deliberately knocking the ball on. The result: a penalty for Leinster and a yellow card for Easter.
Contepomi held his nerve to land the three points on offer and it was very much advantage Leinster at the interval.
Unsurprisingly, they began the second half brimming with confidence and thought they’d scored a try when Rob Kearney crashed over seven minutes after the restart. However, it was disallowed for an alleged forward pass from Contepomi to Isa Nacewa in the build-up.
Leinster were pressing and were pressing but then, in an instant, the momentum shifted dramatically.
Chris Robshaw escaped down the left wing and chipped over the onrushing Contepomi. Then, as Robshaw attempted to round the Argentine, he was felled by Contepomi’s outstretched left leg.
As a result, Contepomi ended up heading for the sin bin just as Easter was leaving it.
Quins boldly opted to turn down the strike on goal in favor of a sustained assault on the Leinster line. The gamble did not pay off, with Stan Wright pilfering possession back for the visitors off the back of an exposed ruck.
Wright intervened again on the hour mark when the Quins pack looked to have driven their way over the whitewash.
However, the replays showed that Wright had gotten his hand in under the ball and the Television Match Official, Derek Bevan, ruled in Leinster’s favor.
Quins kept coming, though, and after a seemingly endless spell of possession, Brown dived over out on the left, much to the delight and the relief of the home fans.
However, Malone, on as a replacement for the injured and out of sorts Evans, failed to convert, meaning Leinster still led.
It went from bad to worse for Quins when Malone was forced off through injury with just under ten minutes to go, leaving Dean Richards’ with no recognized goal-kicker on the field.
As a result, when the Quins pack earned themselves a penalty inside Leinster territory after piling on the pressure at scrum-time there was some confusion as to whether they would go for goal.
Brown, though, was in no doubt that he wanted a crack at the posts. However, while his strike was good, it was not good enough and the ball sailed wide.
Quins' predicament then became somewhat farcical when Williams, Malone's replacement, sustained a bloody lip and had to be withdrawn. That saw Evans, with his heavily bandaged right leg, return to the field.
Somewhat unluckily, it was he who had Quins' last chance to win the game but he dragged a 30-meter drop goal attempt badly wide.
Leinster had survived and their dream of a first-ever Heineken Cup final appearance remains intact.
Standing in their way, Munster. Roll on May 2 at Croke Park.
Harlequins: C Jones; G Botha, M Ross, J Percival, G Robson; C Robshaw, W Skinner; N Easter, D Care, N Evans; U Monye, J Turner-Hall; G Tiesi, D Strettle, M Brown.
Replacements: T Fuga, M Lambert, J Evans, T Guest, A Gomarsall, C Malone, T Williams.
Leinster: R Kearney; I Nacewa, B O'Driscoll, G D'Arcy, L Fitzgerald; F Contepomi, C Whitaker; Cian Healy, Bernard Jackman, Stan Wright; Leo Cullen, M O'Kelly; R Elsom, S Jennings, J Heaslip.
Replacements: J Fogarty, R McCormack, T Hogan, S O'Brien, S Keogh, S Horgan, G Dempsey.