Northampton's indiscipline cost them dearly at Stade Pierre Antoine.
The English side produced a real Jekyll and Hyde performance and were well beaten, with fly-half Steve Myler and flanker Tom Wood both sin-binned in the first and second half.
The French side took full advantage and the English side could not survive playing with 14 men for 20 minutes in this must-win Pool One clash.
Romain Martial scored a brace of tries while Steve Malonga and Ibrahim Diarra also crossed for the hosts.
Northampton also managed four tries of their own with Jamie Elliott (two), Mark Sorenson and Samu Manoa all going over.
In the other Pool One clash, Ronan O'Gara celebrated his 100th Heineken Cup appearance with 12 points as Munster saw off the Scarlets 17-14 at Parc y Scarlets.
The other points for the Irish came with a first-half try for flanker Niall Ronan. It was Munster's 13th straight win over the Scarlets.
The Scarlets, who had a try for flanker Aaron Shingler, two penalties for Rhys Priestland and one for Stephen Jones, led twice but could not match Munster's more streetwise approach.
London Irish kept their hopes alive with a stunning bonus-point 34-14 success over Racing Metro in Pool Two.
A brace of tries in less than five minutes halfway through the second period set the Exiles on their way to their first win of the competition as they bounced back from previous defeats to Edinburgh and Cardiff Blues.
Impressive scores from Joe Ansbro and Adam Thompstone turned the game on its head after 54 and 57 minutes respectively before Thompstone claimed his second with seven minutes remaining at the Stade Yves Du Manoir.
Irish trailed 14-10 at the interval after Jonathan Spratt had matched Sereli Bobo's early effort but there was only one side in it after the break.
Freddie Burns landed the decisive penalty as Gloucester beat Connacht 14-10 for their first win in this season's Heineken Cup.
Burns kicked the English side 6-0 ahead in the Pool Six clash at the Sportsground before James Simpson-Daniel and Connacht captain Gavin Duffy swapped tries coming up to half-time.
The second period was bookended by penalties from Niall O'Connor and Burns as the Cherry and Whites stood firm to pick up only their second away victory in all competitions since February.
In Pool Five, the boot of Kristopher Burton proved the difference as he kicked 16 points to spur Benetton Treviso to an impressive 30-26 win over Biarritz.
The Italian side had gone into the game with an unbeaten home record in the competition and Burton helped them maintain that with three conversions and three penalties.
Early tries by Michele Rizzo and Robert Barbieri were converted by fly-half Burton, before Pelu Taele replied with a try.
Benetton's Cornelius van Zyl and Biarritz's Marcelo Bosch traded tries before Burton kicked a penalty as the home side led 24-12 at the break.
Burton opened up the second half with a penalty but tries from Damien Traille and Yann Lesgourgues and two conversions by replacement Julien Peyrelongue brought the visitors within a point, before Burton's late penalty edged his side to a famous win.
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