Northampton battled hard for an 18-12 Heineken Cup victory over Castres that keeps them in the hunt for quarter-final qualification.
Ulster were confirmed as Pool Four winners following their victory over Glasgow, but Northampton could still reach the knockout stages as one of the best group stage runners-up.
In bitterly cold temperatures and through thickening fog at Franklin's Gardens, Northampton ground out the victory they needed with three penalties each from Stephen Myler and Ryan Lamb.
The Saints will now go in search of a bonus-point victory over Glasgow next weekend and hope that is enough to secure a berth in the quarter-finals.
Ulster reached the quarter-finals for the third successive year with an expected 23-6 victory over Glasgow.
Another triumph next week against Castres will secure a home quarter-final for Mark Anscombe's side.
A first-half try from Nick Williams along with late second-half scores by Jared Payne and Darren Cave secured the four points and with Northampton beating Castres, Ulster progressed after a scrappy game played in difficult conditions at Ravenhill.
The match left the injury-hit Warriors - who were unable to have two prop replacements on their bench - without a win in a miserable season in Europe.
Aviva Premiership strugglers Sale suffered a fourth consecutive defeat by French opposition in the Heineken Cup as Montpellier kept alive their qualification hopes with a bonus-point 27-6 win at the City of Salford Stadium.
With their quarter-final hopes sunk in December by back-to-back defeats by Toulon, Sharks director of rugby Steve Diamond opted to give run-outs to several fringe players and, as expected, they proved no match for their star-studded visitors.
It proved to be a testing debut for number eight Josh Beaumont, the 20-year-old son of former England captain Bill Beaumont, who found himself up against man-of-the-match Johnnie Beattie.
He was a try scorer along with Benoit Paillaugue and Pierre Perard, while the hosts also conceded a penalty try as they could only muster two first-half penalties from Danny Cipriani.
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