Leinster set up an all-Irish final after surviving a late onslaught from Clermont Auvergne during which Wesley Fofana dramatically had a try ruled out for the French side.
Joe Schmidt's side started the game well but with their lineout malfunctioning, four penalties from Brock James saw the French challengers lead 12-6 at half-time.
Yet Leinster got the perfect start to the second half when Brian O'Driscoll and Rob Kearney combined to set up Cian Healy for a 42nd-minute try.
A stunning Kearney drop goal extended Leinster's lead before James replied. Jonathan Sexton's third penalty put Leinster 19-15 in front before Clermont centre Fofana was inches away from scoring the match-winning try.
This pulsating semi-final finished with Clermont pounding the Leinster line but the Irish side showed immense resilience to hold on and set up a meeting with Ulster at Twickenham on May 19.
After a typically frenetic opening, Leinster struck first in the eighth minute. Some quick offloading got Leinster into the Clermont 22 for the first time and the hosts were punished for offside as the onrushing Isa Nacewa accepted a pass out wide from Sexton. The fly-half slotted the penalty over to give the province the early advantage.
Some ferocious work by Leinster was resulting in turnover ball and Clermont suffered another blow when winger Julien Malzieu was forced off through injury after 13 minutes.
There was a superb atmosphere in the Stade Chaban-Delmas, although the Irish support was vastly outnumbered in the near 33,000 crowd. But competing in their fourth successive semi-final, Leinster's experience was showing in the early stages.
More quick hands from the Leinster back-line led to another break for Nacewa that had Clermont scrambling to clear from behind their own posts.
But Clermont's defence held firm and James took the chance to tie things up at 3-3 from a penalty.
That lifted the 2010 French champions and only a fantastic intervention by Luke Fitzgerald denied full-back Lee Byrne a try after slick handling by Nathan Hines and Lionel Faure.
Leinster contained another Clermont assault on 22 minutes but their captain Leo Cullen was fortunate to escape without being yellow carded after a scuffle with Lionel Faure.
Vern Cotter's men were shifting through the gears and only more frantic defending saw the holders cling on, only for James to boot Clermont ahead after 31 minutes.
Leinster responded instantly when Sexton kicked his second penalty after Nacewa was impeded, but James had the final say of the first half - firing over two more penalties to give Clermont a 12-6 buffer at the break.
The interval clearly came at a good time for the defending champions though as they responded just after the restart with the opening try.
With their lineout working for once, O'Driscoll and Kearney punched a hole through the Clermont defence to give Healy an easy run-in. Sexton converted and Leinster were a point ahead.
Four minutes later they went 16-12 in front when the increasingly influential Kearney produced a stunning drop goal from over 45 metres out.
James then missed a drop goal and a penalty in quick succession before another penalty from the Australian made it 16-15 after 52 minutes.
Both sides emptied their benches in an attempt to force a decisive shift in momentum and O'Driscoll almost delivered it after finding space to feed Kearney.
Although Leinster were held up a few metres out, Clermont had infringed and Sexton kicked over from a tricky angle outside the 22 to make it 19-15 with 17 minutes left.
Leinster appeared to be getting stronger as the game went on but after Sexton missed another penalty attempt there was to be a further twist as Clermont's forwards pushed for a winning try.
Fofana appeared to have got it with seconds remaining but after television match official Geoff Warren reviewed the footage, the try was ruled out for a knock on. The French international fumbled the ball forward under pressure from Gordon D'Arcy's last-ditch tackle.
Clermont had another five-metre scrum before the end but Leinster, backing their spirited defence, somehow escaped to move a step closer to back-to-back European titles and their third success in four years.
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