Harlequins' Heineken Cup hopes were dealt a severe blow when visiting Castres convincingly overturned the south London side 39-17.

The result leaves John Kingston's side with only one victory from three European outings and in desperate need of a win at Castres next week.

Scotland international Gregor Townsend was inspirational for the French side, kicking five penalties and two conversions with fellow Scot Shaun Longstaff and Kiwi Norman Berryman also on the scoreboard.

Quins had started well with a Dan Luger try after just five minutes. England international Will Greenwood fed the winger who side-stepped his way through Castres defence to touch down.

Mark Mapletoft, standing in for the injured Paul Burke, converted but Castres soon bounced back with two penalties from the boot of Townsend.

Mapletoft added another penalty but that proved to be Harlequins' last score for more than an hour as the visitors put their foot down and took charge.

After 13 minutes Longstaff scored a superb try on the right wing after centre Eric Artiguste and Berryman had combined to split the Quins defence.

Townsend missed the conversion but made amends with two further penalties to put the visitors 17-10 ahead.

It was then Berryman's turn to get on the scoreboard when he crossed the line after Townsend had brilliantly switched the play wide. Townsend once again converted to put his side 24-10 ahead at the break.

Winger Longstaff notched up his second try of the afternoon before Kiwi Berryman matched his effort giving Castres a massive 26-point lead.

Forward Steve White-Cooper salvaged some pride for the home side as he sneaked around the blindside of a ruck 45 metres upfield for a converted try with just eight minutes remaining.

But a fifth Towsend penalty for Castres sealed their triumph.