|Toulon (6) 25|
|Try: Habana Con: Halfpenny Pens: Halfpenny 6|
|Leinster (9) 20|
|Try: O'Brien Pens: Madigan 5|
Toulon will go for a hat-trick of European titles after Bryan Habana's interception try secured a nerve-shredding extra-time win over Leinster.
In greasy conditions, four kicks apiece from Leigh Halfpenny and Ian Madigan made it 12-12 after 80 minutes.
Halfpenny kicked Toulon ahead, but they then lost Ali Williams to the sin bin.
With a man advantage, Leinster attacked - but Habana picked off a Madigan pass to score, and Sean O'Brien's try could not deny the defending champions.
After an ugly, error-strewn opening 80 minutes in Marseille, a game that had been dominated by crunching defence and the boots of Halfpenny and Madigan turned into a drama of operatic proportions.
Despite having the better of territory and possession, Toulon had been unable to shake off a dogged Leinster side.
At the moment Halfpenny's fifth penalty looked to have given Bernard Laporte's team the advantage, they lost former All Blacks lock Williams to the bin after he made contact with Devin Toner as the 6ft 10in Irish lock soared to take a kick.
Leinster went on the attack but Madigan's attempt to release the Dublin-based side down the right only set up Habana to race home from halfway for the decisive score.
That secured a final against fellow French side Clermont at Twickenham on 2 May - a repeat of the final two years ago, which Toulon won 16-15.
It was fitting that the game turned into such an epic encounter because the two sides have been kings of Europe five times between them in the past six seasons.
Leinster have since dropped away slightly from the summit of the European game and two-time defending champions Toulon, boosted by playing an hour down the road from their home on the Mediterranean coast, were strong favourites.
But despite having a galaxy of global stars in their line-up, they could not shake off Leinster, who led 9-6 at the break.
Halfpenny's boot put Toulon in front in the second half, but Madigan made it 12-12 to send the game into extra time as the sun finally appeared.
As the tension increased by the second, two Halfpenny penalties to one by Madigan made it 18-15 with 10 minutes remaining, before Williams blotted his copybook and referee Wayne Barnes, operating as ever by the letter of the law, sent the ex-New Zealand lock to the bin.
Leinster spied their chance but there is no better poacher of interceptions in the game than Springbok great Habana.
He picked off Madigan's loopy pass before showing that even at the age of 31 - positively ancient for a winger - he had more than enough pace to make sure Leinster were never going to catch him.
Halfpenny was again on target with the conversion to take the lead out to what was surely a match-winning 10 points but Leinster were not beaten yet.
A turbo-charged line-out drive sent Ireland flanker O'Brien plunging over but Toulon kept Leinster at arm's length in the closing seconds and are one win away from an unprecedented three straight European titles - something not even Leinster, who were champions three times in four years - managed to achieve.
Toulon: Halfpenny; D Armitage, Bastareaud, Giteau, Habana; Michalak, Tillous-Borde; Chiocci, Guirado, Hayman, Botha, Williams, J Smith, Fernandez Lobbe, Masoe.
Replacements: Armitage for J Smith (35), Mitchell for Habana (91), Wulf for Michalak (48), Menini for Chiocci (51), Orioli for Guirado (68), Chilachava for Hayman (75), Suta for Botha (61).
Not Used: Claassens.
Sin Bin: Williams (86).
Leinster: R Kearney; McFadden, Te'o, Madigan, Fitzgerald; Gopperth, Boss; Healy, Cronin, Ross, Toner, M McCarthy, J Murphy, O'Brien, J Heaslip.
Replacements: Kirchner for McFadden (61), Reddan for Boss (66), J McGrath for Healy (66), Strauss for Cronin (66), Moore for Ross (57), Marshall for M McCarthy (91), D'Arcy for Gopperth (90).
Not Used: Ryan
Ref: Wayne Barnes (RFU).