The Wanderers booked a home semi-final in the Aviva ‘A’ League – despite losing 30-24 at Gloucester on Monday night.
The losing bonus point, secured by a late try from hooker Matt Williams, was enough to clinch top spot and set up a final-four clash at Franklin’s Gardens.
The Wanderers side, which included Gerrit-Jan van Velze, making his return to action after a four-week ban, had gone 13-0 down early on at Kingsholm.
And they really looked to have their work cut out when Noah Cato was shown a yellow in the 19th minute.
But the away side refused to crumble and a try from scrum-half Alex Day, followed by a Will Hooley conversion, got them back in the game.
Gloucester then stretched their lead to 18-7 through Ian Clark’s first try of the night, but Cato made amends for his sin-binning to pull the Wanderers back to within six.
Clark got another score just before the break to leave the Northampton side with it all to do in the second half, but they battled bravely to grab two further tries.
The first came from England Under 20 wing Tom Collins and after Elliott Stooke had added another for the Cherry and Whites, Williams popped up to ensure the Wanderers finished top of the pile.
Wanderers: Cato; Armstrong, Stephenson, Burrell, Collins; Hooley, Day; E Waller, McMillan, Herriott; Hicks, Woolford; Nutley, Harrison, van Velze. Replacements: Williams, Hobbs, Rhodes, Hopley, Warr, Glynn, Wootton, Mogensen