Saints trailed 15-0 before they turned the Pool Four clash on its head through three tries in six minutes either side of half-time.
Centre George Pisi touched down twice, while fly-half Stephen Myler's try just after the break nudged Northampton ahead for the first time before wing Vasily Artemyev's late effort sealed it.
Myler and Ryan Lamb each booted a conversion to help wipe out a deficit as Saints conceded tries to Glasgow flanker Josh Strauss and wing Sean Lamont after Peter Horne kicked an early penalty and converted Strauss' try.
Danny Cipriani was Sale Sharks' hero as the Premiership strugglers overturned a 27-12 deficit to gain a dramatic, morale-boosting 34-33 triumph over Cardiff Blues.
The Sharks were trailing by 15 points when Cipriani was introduced from the bench after 49 minutes and he scored one try and created another as Bryan Redpath's men went on to snatch a breathless victory.
Cardiff, who played all but five minutes of the match without Sam Warburton due to injury, were still leading 30-24 when they were reduced to 14 men with the sin-binning of replacement Lewis Jones seven minutes from the end.
And the extra man advantage proved crucial as former Munster prop Tony Buckley was driven over for the match-winning try a minute later, although the Sharks were hanging on in the end after Leigh Halfpenny's seventh goal from as many attempts had cut the gap to a solitary point.
The outcome was tough on Wales winger Alex Cuthbert, whose first-half hat-trick of tries looked to have put his side on their way to victory.
Two-time Heineken Cup champions Leicester could not pick up a point from their opening Pool Two match against Toulouse after a 23-9 defeat in the south of France.
The Tigers were only 11-9 behind at the break but the kicking prowess of Luke McAlister won the day for the home side with his boot accounting for 18 points, with centre's Gael Fickou's first half try the only of the game.
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The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
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