Image source, Getty Images. BySteve Mather. BBC Sport journalist. 9 hours ago. 134 Comments. Investec Champions Cup. Northampton Saints (14) 49. Tries: Penalty try, Fischetti, Kemeny, Freeman, Furbank, McParland, Dingwall Cons: Belleau 6. Castres (15) 41. Tries: Ambadiang 2, Chabouni, Ardron, Karawalevu, Botitu Cons: Fernandez, Herve 3 Pen: Fernandez. Northampton were given a stern examination of their Champions Cup credentials by impressive Castres as they came out on top of an engrossing contest to book their place in the quarter-finals.. Saints were 12-0 down after 11 minutes as Christian Ambadiang and Theo Chabouni stunned the home side, before a penalty try and yellow card to Ambadiang gave the hosts a route back into the game.. Northampton prop Danilo Fischetti powered over but Saints trailed 15-14 at the break, taking the lead for the first time thanks to Josh Kemeny early in the second period after some fine footwork from captain George Furbank.. From there the tries flowed freely from both sides, with Tommy Freeman and Furbank’s scores replied to by Tyler Ardron and Vuate Karawalevu.. Fraser Dingwall’s try finally pushed Saints out of range but Castres scored the last of the 13 tries when Ambadiang raced away for his second as the French Top 14 side pushed Prem leaders Northampton all the way to the final whistle.. Phil Dowson’s side will face the winner of Saturday’s all-English contest between Bath and Saracens in next weekend’s quarter-final.. Image source, Getty Images. Castres’ line speed and pressure on passes forced Saints into some early handling errors, one of which led to the visitors taking a deserved lead after eight minutes.. Scrum-half Jeremy Fernandez took the ball from a scrum and broke down the blind side before putting a perfectly weighted kick behind the Saints defence for winger Ambadiang to race onto and score.. They had a second soon after when Ambadiang intercepted a loose pass and the ball was moved wide for Chabouni to stride over and make it 12-0.. Saints were on the board after 15 minutes with a penalty try for an Ambadiang high tackle on Archie McParland as he looked set to score, with the Castres winger yellow-carded.. They were down to 13 men after 18 minutes when lock Guillaume Ducat recklessly cleared out Henry Pollock at a ruck but they stretched their lead despite their numerical disadvantage with a Fernandez penalty before Saints hit back through Fischetti.. Castres took a one-point lead into the break but the hosts went in front for the first time two minutes into the second half when Furbank created space for Kemeny to dive over.. Last season’s runners-up Saints seemed to seize control of the contest when Furbank sent Freeman over the line to make it 26-15 but Ardron intercepted McParland’s pass to fire back immediately and keep Castres in the contest.. The home crowd was left stunned as Karawalevu powered over from first-phase ball to make it 28-27 in the 56th minute and the winger thought he had ano