Dan Biggar kicked seven penalties to help Ospreys to a 21-12 Heineken Cup victory over Castres at Liberty Stadium on Friday.
The Ospreys dealt Castres' hopes of qualification for the play-offs a severe blow by recording their first win of the competition.
The Frenchmen haven't won away in the Heineken Cup since 2007 and they didn't get off to the best of starts in south Wales even prior to kick off, having to borrow some white socks from the home side to make it easier to distinguish between their dark blue kit and the black of the hosts.
They did register the first points of the match in the opening five minutes though via the boot of last season's top points scorer in the Top 14, Rory Kockott.
He and Welsh international fly-half Biggar kicked four penalties apiece during the first half as neither side was able to gain a stranglehold in the match.
The hosts will be disappointed not to have taken a lead into the half-time break though as they had the benefit of playing against 14 men for 10 minutes when France fly-half Remi Tales was sent from the field for an infringement at the breakdown.
The rain began to fall heavily after the restart and the Ospreys dealt with the conditions better than their visitors and took advantage of the French Top 14 champions' ill-discipline inside their own half.
Biggar continued his excellent form with the boot and it may not have been pretty but three further penalties at regular intervals ensured that the Welshmen were more than one score ahead with 10 minutes remaining.
Castres pushed hard in the closing stages, with the result far more important to them, but the home side were resolute and repelled every attack to maintain their unbeaten record against French opposition at the Liberty Stadium and do Leinster and Northampton a big favour ahead of their meeting on Saturday.
Pens: Biggar 7
Pens: Kockott 4
Yellow card: Tales
Ospreys: 15 Sam Davies, 14 Aisea Natoga, 13 Tom Isaacs, 12 Ben John, 11 Jeff Hassler, 10 Dan Biggar, 9 Rhys Webb , 8 Ryan Jones (c), 7 Justin Tipuric, 6 Sam Lewis, 5 James King, 4 Tyler Ardron, 3 Aaron Jarvis, 2 Richard Hibbard, 1 Ryan Bevington.
Replacements: 16 Scott Baldwin, 17 Marc Thomas, 18 Dan Suter, 19 Sam Williams, 20 Morgan Allen, 21 Tom Habberfield, 22 Matthew Morgan, 23 Tom Grabham.
Castres: 15 Geoffrey Palis, 14 Marcel Garvey, 13 Remi Lamerat, 12 Paul Bonnefond, 11 Remi Grosso, 10 Remi Tales (c), 9 Rory Kockott, 8 Antonie Claassen 7 Yannick Caballero, 6 Jannie Bornman, 5 Rodrigo Capo Ortega, 4 Richie Gray, 3 Anton Peikrishvili, 2 Marc-Antoine Rallier, 1 Yannick Forestier.
Replacements: 16 Brice Mach, 17 Saimone Taumoepeau, 18 Michael Coetzee, 19 Christophe Samson, 20 Ibrahim Diarra, 21 Julien Tomas, 22 Daniel Kirkpatrick, 23 Max Evans.
Venue: Liberty Stadium
Referee: Luke Pearce (England)
Assistant referees: Dean Richards, Robin Goodliffe (both England)
TMO: Geoff Warren