A late second half try from Castres left winger David Smith saw them beat Grenoble 33-28 in the Top 14 on Friday.
The home side crossed the whitewash for the first and only time in the 77th minute, through a late converted try from right winger Tino Nemani, but the educated boot of Jonathan Wisniewski however kept Grenoble's side of the scoreboard ticking over.
Despite being successful with four second half penalties the 30-year-old fly-half's fine form from the tee was not enough for Grenoble as the visitors bagged a valuable win.
This win means that Castres move seven points clear of Grenoble on the Top 14 table and find themselves hot on the heels of Toulouse.
The boot of Ben Urdapilleta was as accurate as his opposite number, with the Castres playmaker slotting early penalties and converting all of their tries.
Wisniewski drew first blood in the 7th minute when he succeeded with an early penalty conversion to make the score 3-0. He would go on to add an additional two first half penalties.
However two first half tries from Thomas Combezou and Alex Tulou was converted by Urdapilleta to make the score 17-9 as the players headed into the locker rooms for half-time.
It was Wisniewski that dealt the first blow in the second half again succeeding with two penalties, the playmaker made it a two-point game with the score on 17-15.
The playmakers subsequently exchanged a further three points each as the hour mark was approaching.
The kicking contest would continue between Wisniewski and Urdapilleta as they exchanged a penalty each with the latter getting an additional penalty to nudge the scoreboard to 26-21 as the match entered the final ten minutes.
Castres' third try from Smith was scored on the 71st minute, Urdapilleta converting and extended the lead to 33-21.
At this point the game looked out of reach for the home side with Castres enjoying a comfortable twelve-point lead.
The 77th minute try from right winger Nemani breathed some hope back into the home side as the replacement Gilles Bosch added the extras to make the score 33-28 with three minutes left.
This was however a little too late as the final score of the match remained on 33-28 as Castres bagged an important away win.
Pens: Wisniewski 7
Yellow Card: De Klerk
Tries: Combezou, Tulou, Smith
Cons: Urdapilleta 3
Pens: Urdapilleta 4
Yellow Cards: Caballero, Tichit
Grenoble: 15 Gio Aplon, 14 Tino Nemani, 13 Chris Farrell, 12 Fabrice Estebanez, 11 Lucas Dupont, 10 Jonathan Wisniewski, 9 Charl McLeod, 8 Steven Setephano, 7 James Hart, 6 Mahamadou Diaby, 5 Mathias Marie, 4 Peter Kimlin, 3 Rossouw De Klerk, 2 Loick Jammes, 1 Fabien Barcella
Replacements: 16 Paulin Mas, 17 Sona Taumalolo, 18 James Percival, 19 Henry Vanderglas, 20 Lilian Saseras, 21 Gilles Bosch, 22 Nigel Hunt, 23 Dayna Edwards
Castres: 15 Geoffrey Palis, 14 Julien Caminati, 13 Thomas Combezou, 12 Rémi Lamerat, 11 David Smith, 10 Ben Urdapilleta, 9 Rory Kockott, 8 Alex Tulou, 7 Mathieu Babillot, 6 Yannick Caballero, 5 Rodrigo Capo Ortega, 4 Richie Gray, 3 Yohan Montes, 2 Marc-Antoine Rallier, 1 Antoine Tichit
Replacements: 16 Julien Beziat, 17 Mihai Lazar, 18 Christophe Samson, 19 Johnnie Beattie, 20 Antoine Dupont, 21 Julien Dumora, 22 Florian Vialelle, 23 Lucas Martinez
Referee: Cyril Lafon