Having gone down to 14 men after just 12 minutes, Racing 92 came from 21-05 down to edge past Connacht Rugby 43-40 at The Sportsground.
Four tries apiece in the first half meant Connacht took a slender 4-point advantage into the break, but Owen Farrell came on after 47 minutes and had an immediate impact.
He took the French upfield to score a minute after taking to the pitch, before slotting a drop goal to put them 37-28 up.
Two more penalties from Nolann Le Garrec to add to his two tries were enough to see Racing over the line and into the semi-finals, despite two late tries from the hosts to test the nerves.
Scorers:
Connacht Rugby: Tries: Penalty try, Bundee Aki, Cian Prendergast (2), Ben Murphy, Cathal Forde. Conversions: JJ Hanrahan (4),
Racing 92: Tries: Wame Naituvi, Diego Escobar, Nolann le Garrec (2), Josua Tuisova. Conversions: Dan Lancaster (2), Nolann le Garrec. Penalties: Dan Lancaster, Nolann le Garrec (2). Drop Goal: Owen Farrell.
Teams
Connacht Rugby: 15 Mack Hansen, 14 Shane Jennings,13 Hugh Gavin, 12 Bundee Aki, 11 Finn Treacy, 10 JJ Hanrahan, 9 Ben Murphy, 8 Sean Jansen, 7 Shamus Hurley-Langton, 6 Cian Prendergast (c), 5 Joe Joyce, 4 Josh Murphy, 3 Finlay Bealham, 2 Dave Heffernan, 1 Denis Buckley. Replacements: 16 Dylan Tierney-Martin, 17 Peter Dooley, 18 Jack Aungier, 19. Oisín Dowling, 20 Paul Boyle, 21 Matthew Devine, 22 Josh Ioane, 23 Cathal Forde.
Racing 92: 15 Sam James, 14 Wame Naituvi, 13 Vinaya Habosi, 12 Josua Tuisova, 11 Max Spring (c), 10 Dan Lancaster, 9 Nolann le Garrec, 8 Jordan Joseph, 7 Junior Kpoku, 6 Maxime Baudonne, 5 Will Rowlands, 4 Boris Palu, 3 Demba Bamba, 2 Diego Escobar, 1 Eddy Ben Arous. Replacements: 16 Robin Couly, 17 Guram Gogichasvili, 18 Leota Lehopame, 19 Tomain Taofifenua, 20 Shinbgirai Manyarara, 21 Donovan Taofifenua, 22 Owen Farrell, 23 Henry Chavancy.