Saints were forced to stand up for the Ulstermen after the Irish side clinched a crucial 25-6 Heineken Cup win at Franklin’s Gardens on Friday night.
Ulster, who have now won all 13 of their games this season, were a cut above in attack as they left Saints’ hopes of progressing to the knockout stages in tatters.
Tries from Andrew Trimble and Tommy Bowe sent Mark Anscombe’s men in 13-6 up at the break, with Ryan Lamb, who struggled with the boot, registering two penalties for Saints.
And the Irishmen continued to prove incisive after half-time, picking up a try bonus point as Jared Payne and, with a minute to go, Dan Tuohy cruised across the whitewash.
Tuohy’s try came despite the sin-binning of hugely influential back-row forward Ian Henderson and Ulster walked away with all five points.
For Saints it was a sobering night as they hit a brick wall against a side fancied to go all the way in Europe’s premier competition this season.
Similar shutouts hurt Jim Mallinder’s men against the likes of Leicester and Saracens and the addition of a new backs coach may be required sooner rather than later.
As it is, Saints will travel to Belfast next weekend needing to fight for their Heineken Cup lives, knowing only the biggest of wins will be good enough.
Former Saint Roger Wilson was left smiling at the final whistle, and he had earlier received a warm welcome on his first return to the Gardens since departing during the summer.
But once the necessary pre-match pleasantries had been exchanged, it was down to business.
The opening minutes saw some ferocious scrummaging, with both sides standing strong.
Saints were the ones to show their teeth first as Ken Pisi won a penalty out wide, but Lamb shanked it.
Back came Ulster and they went straight for the jugular as fly-half Paddy Jackson pulled the strings, chipping through for Trimble to touch down.
Jackson missed the conversion and Lamb was having similar struggles at the other end, failing making the most of a push from the forwards, who had secured a penalty.
Both fly-halves were still searching for their shooting boots as Jackson also made it none from two, flicking a penalty from inside halfway wide of the uprights.
It was becoming a tale of two tens and Lamb finally put his name on the scoresheet, landing a penalty from just inside halfway.
This time, Jackson replied, striking the ball sweetly from the tee to put Ulster 8-3 up and Lamb missed the chance to reply, failing with a drop goal before firing a penalty wide.
And the Irish invaders made the Saints fly-half pay for his profligacy in front of the posts, working through the phases and sending Bowe over in the corner.
Jackson again fluffed the kick as his kicking copybook continued to be blotted, while Lamb finally got back on the board to send his side in at half-time 13-6 down.
But Ulster’s charge towards a big triumph wasn’t to be stopped, certainly not by the Saints defence, who crumbled in the face of Payne, who strolled through to score.
Jackson made it 20-6 to the RaboDirect PRO12 table-toppers, whose vociferous travelling fans were in dreamland.
Lee Dickson was sent on to try to inject some urgency into Saints, and how they needed it.
But Ulster continued to hold the upper hand, remaining defiant in defence as the home side failed to find the thrust they needed to get over the tryline.
Dickson came close, surging through, only to be held up in agonising fashion by opposition scrum-half Ruan Pienaar.
Ulster lost hugely influential forward Ian Hendenson to a sin binning before the end, but it made no difference as Tuohy flew over to seal all five points.
Jackson missed the conversion but Ulster had what they needed, leaving Northampton with smiles etched on their faces.
Saints: Foden; K Pisi, G Pisi, Waldouck (May 67), Elliott; Lamb (Myler 60), Roberts (Dickson 52); Tonga’uiha (A Waller 64), Hartley (Haywood 72), Mujati (Doran-Jones 60); Manoa, Lawes; Clark (Dowson 57), Wood, van Velze.
Ulster: Payne; Bowe, Cave, Wallace (L Marshall 70), Trimble (Gilroy 70); Jackson, Pienaar; Court, Best, Afoa; Muller (Williams 50), Tuohy; Henderson, Henry, Wilson.
Replacements: Brady, Black, Lutton, Diack, P Marshall.
Referee: Jerome Garces (FFR)