Harlequins pushed Castres all the way but finally succumbed as their hopes of reaching the Heineken Cup quarter-finals faded at the Stade Pierre-Antoine.

Mike Slemen got Harlequins off to a good start with a penalty in the first minute.

But Castres centre Eric Artiguste powered his way across the line just outside the 22, and Romaine Teulet converted to put the home side ahead.

After a 40-yard surge from Steve White-Cooper, Slemen neatly chipped the ball into the right-hand corner and Keith Wood picked up the bouncing ball two yards out and ran over.

Slemen added a superb 42-yard angled penalty after 15 minutes to extend the visitors' lead and for the remainder of the half Harlequins looked very comfortable at 11-7 ahead.

But two minutes before the break, Olivier Sarramea chased a neat grubber kick from Raphael Ibanez and won the race to the loose ball to score, with Teulet's conversion putting the home team in front again.

In the second half Quins fell further behind to a Romain Teulet penalty after 49 minutes when Will Greenwood conceded a needless penalty.

A minute later, Castres full-back Ugo Mola took advantage of a turnover under the Quins posts and Teulet again converted.

Harlequins nearly scored four minutes later after centre Nick Greenstock's pass gave Matt Moore a chance.

They had more success later when the ball was spread from a line-out to Moore.

His inside pass allowed centre Greenwood in for a try and Slemen's conversion set up an exciting finish.

Ben Gollings and Slemen both had chances to add to Quin's tally in an end-to-end finale but Castres held out for victory.

Castres
Tries: Mola, Artiguste, Sarramea.
Cons: Teulet 3.
Pens: Teulet.

Harlequins
Tries: Greenwood, Wood.
Cons: D Slemen.
Pens: D Slemen 2.

Castres: Mola, Longstaff, Artiguste, Berryman, Sarramea, Teulet, Albouy, Toussaint, Ibanez, Moyle, Dourdet, Spanghero, Costes, Lassissi, Taussac. Replacements: R. Vigneaux, Tsabadze, Laluque, Froment, Gargallo, Delmotte, Caussade.

Harlequins: O'Neill, Moore, Greenwood, Greenstock, Luger, D Slemen, M Powell, Starr, Wood, Leonard, Morgan, Davison, White-Cooper, Sanderson, Winters. Replacements: Fuga, Douglas, Tamarua, Diprose, Bemand, Burrows, Gollings.

Referee: Nigel Williams (Wales)