Castres jumped ahead of the Saints thanks to a hat-trick of penalties from South African scrum-half Rory Kockott at Scotstoun.

Kockott missed four more penalties at Glasgow's new home but his two first-half strikes and a match-winning effort after 57 minutes mean Castres could now harbour realistic hopes of pushing Ulster for top spot when the pool leaders head to France in Round 6.

Glasgow twice led through the boot of fly-half Scott Wright on 13 and 23 minutes but Kockett pegged the Warriors back as the game hit the 20-minute mark and then again four minutes before the interval.

Wright missed a straightforward chance to make it 9-6 to the hosts on 48 minutes and Kockott made him pay nine minutes later.

Neither side could summon up what would have been a game-changing try, although it was Castres who came closest as they twice enjoyed spells of possession just metres from the Glasgow line only to concede penalties at the pivotal moments.

Their failure to kill the game off with a seven-pointer made no difference on a freezing Scottish evening, though, as Glasgow were unable to find the score that would have stopped them from slipping to a third successive European defeat this term and a fifth Heineken Cup reverse in a row since their draw with Montpellier 12 months ago.