Hook's 17 points looked good
Jerome Porical kicked a dramatic late winner to send Stade Francais Paris to their second European Challenge Cup Final in three years.
The Stade fullback struck twice from distance in the Final seven minutes to stun Perpignan with a 25-22 win at Stade Aime Giral.
James Hook's 17 points looked like sending Perpignan to their first European Final in 10 years.
But Porical held his nerve to level the scores with a giant kick from inside his own half and then strike a winner of both the post and crossbar to snatch victory.
It capped a stunning man of the match display by Porical, who also scored Stade's first try before David Lyons followed, and sent Stade Francais into the May 17 Final in Dublin.
It was a case of more heart-ache for Perpignan who were roared on by a raucous home crowd as they chased only their second European Final appearance.
But Stade proved capable of winning away from home with their quarter-final win at Bath and silenced Stade Aime Giral after seven minutes with Porical's penalty.
Perpignan struck back almost immediately with the game's opening try.
Farid Sid kicked ahead and Perpignan poured forward to recover possession close to Stade's try line before Lifeimi Mafi's long pass found Guilhem Guirado out wide and the hooker was not to be denied from 10 metres out.
Hook missed the conversion but touched down moments later in exactly the same spot as Perpignan seized control.
Scrum-half Florian Cazenave and Sid combined before Hook switched the direction of the attack. Only good defence denied Adrien Plante but Hook scooped up and dived over in the corner.
Again the conversion was narrowly wide and Perpignan were left to hope they would not regret the missed points as Stade edged the exchanges up front for Porical to cut the lead to 13-9 by half-time.
Hook opened some daylight early in the second half after the video official ruled his penalty had dissected the posts, but the gap was slammed shut when Lyons stormed over moments later.
However it was the wonderful balance and speed of Porical that did the damage after evading three Perpignan defenders before finding the former Wallaby with a hopeful inside pass.
Porical's conversion levelled the scores and he did so again on 52 minutes after Hook had closed in on 300 career points in Europe with his third penalty.
Both kickers missed their next chances as nerves grew and the scoring chances dried up amid the tension.
Hook nudged Perpignan ahead - again with the help of the video official after the touch judges ruled his lofty kick wide - on 68 minutes.
But Stade held both their nerve and the edge up front to hand Porical two half chances that he took in style.
Tries: Guirado, Hook
Pens: Hook 4
For Stade Français:
Pens: Porical 6
Perpignan: 15 Gavin Hume, 14 Farid Sid, 13 David Marty, 12 Lifeimi Mafi, 11 Adrien Plante, 10 James Hook, 9 Florian Cazenave, 8 Henry Tuilagi, 7 Luke Narraway, 6 Alasdair Strokosch, 5 Romain Taofifenua, 4 Dan Leo, 3 Kisi Pulu, 2 Guilhem Guirado, 1 Sona Taumalolo.
Replacements: 16 Romain Terrain, 17 Sebastien Taofifenua, 18 Jerome Schuster, 19 Guillaume Vilaceca, 20 David Mélé, 21 Sione Piukala, 22 Joffrey Michel, 23 Bertrand Guiry.
Stade Français: 15 Jerome Porical, 14 Jérémy Sinzelle, 13 Geoffrey Doumayrou, 12 Paul Williams, 11 Hugo Bonneval, 10 Jules Plisson, 9 Julien Dupuy, 8 Sergio Parisse , 7 Pierre Rabadan, 6 David Lyons, 5 Scott Lavalla, 4 Gerhard Mostert, 3 Rabah Slimani, 2 Laurent Sempere, 1 Aled de Malmanche.
Replacements: 16 Remi Bonfils, 17 Stanley Wright, 18 Jérémy Becasseau, 19 Anton van Zyl, 20 Antoine Burban, 21 Nicolas Bezy, 22 Paul Warwick, 23 Julien Arias,
Referee: George Clancy (Ireland)
Assistant referees: Dudley Phillips (Ireland), Marius Mitrea (Italy)
TMO: Jim Yuille (Scotland)