A second-half comeback saw London Irish win in Paris to keep their faint hopes of Heineken Cup qualification alive.
Racing led 14-3 via two Gaeton Germain penalties, a Sereli Bobo try and a drop-goal from Jonathan Wisniewski.
But Jonathan Spratt's converted try gave Irish hope before half-time, and further scores from Joe Ansbro and Adam Thompstone took them 27-14 clear.
Thompstone's second try with seven minutes left brought the Exiles a welcome bonus point.
They will still need to win their remaining three pool games to have any chance of qualifying as one of the two best runners-up, with the return fixture against Racing next Saturday.
Racing Metro 92: G Germain; S Bobo, V Vakatawa, J Matavesi, J Imhoff; J Hernandez, M Loree; J Brugnaut, T Bianchin, J Orlandi, L Nallet [capt], J Nailiko, A Batut, B Le Roux, J Cronje.
Replacements: G Arganese, E Ben Arous, J Coetzee, F van der Merwe, S Descons, J Wisniewski, J Leo'o, S Chabal
London Irish: Delon Armitage, Topsy Ojo, Joe Ansbro, Jonathan Spratt, Adam Thompstone, Dan Bowden, Darren Allinson; Clarke Dermody, David Paice, Paulica Ion, Bryn Evans, Matt Garvey, Declan Danaher, Ofisa Treviranus, Chris Hala'ufia.
Replacements: Brian Blaney, Max Lahiff, Faan Rautenbach, Bob Casey, Jamie Gibson, Tom Homer, Adrian Jarvis, Paul Hodgson.