Saints sunk by old rivals Castres on humbling afternoon in France
Castres ran in five tries in a 41-7 demolition of old European rivals Northampton courtesy of a dominant forward performance that saw the visitors' pack shoved all over the park.
Winger David Smith was the main beneficiary of the hosts' total control up front in the ninth European meeting between the two sides.
He touched down twice - the first a saunter under the posts after captain Alex Tulou's powerful run punched a hole in the Saints' defence after 31 minutes, while his second came four minutes into the second period when he danced past two defenders to score in the corner following a smart offload from Thomas Combezou.
Smith should have notched his hat-trick little more than a minute later, but he was unable to hold on to a sleight-of-hand pass from Tulou with his route to the line clear,
Smith's brace sandwiched a try for loosehead prop Antoine Tichit, who was shoved over the line by his forward colleagues. Benjamin Urdapilleta converted both - the last with a little help from the upright.
Saints had turned down four relatively straightforward penalty chances in favour of kicks to the corner during a period of concerted pressure midway through the first half.
But they were unable to make their possession tell, despite crossing the Castres line. After consulting with the TMO the referee ruled the ball was held up - and the hosts simply shoved the Saints pack off the ball from the resulting five-metre scrum.
It was not the first time the Saints' pack - featuring Courtney Lawes, Tom Wood, Teimana Harrison, Louis Picamoles and the returning Dylan Hartley - had been embarrassed.
The hosts' forwards were on a mission to prove that last week's dismantling at Leinster was an aberration. They pushed the Northampton unit off the ball time and time again. And captain Tulou was causing mayhem whenever he had the ball in hand.
Not even a yellow card for scrum-half Rory Kockott seemed to alter the game plan - or affect their control. In fact, it appeared to galvanise the home side's determination to prove that last week's five-try drubbing by Leinster in Dublin was an aberration.
Northampton arrived seeking their first back-to-back wins over French opposition since 2011/12 following last week's last-gasp win against Montpellier, but in the second half they were consigned to the role of doughty defenders.
They barely broke into Castres territory in the opening quarter of the second half - and even when they managed to get over the gainline, they were held at bay by an organised Castres defence.
The game was long over as a contest by the time Saints' winger James Wilson touched down for a consolation try with eight minutes left on the clock.
There was still time for Castres to notch two more tries. Fittingly, it was a forward who scored the bonus-point try. Replacement flanker Alex Bias charged over in the corner after Northampton ran out of defenders.
And the home fans' celebrations were well under way when 19-year-old replacement scrum-half Antoine Dupont picked up a pass-off-the-floor from man-of-the-match Smith to burst clear for Castres' fifth.