Saints will finish top of the Aviva Premiership for the first time after cruising to a bonus-point 46-0 win against London Welsh.
The Franklin’s Gardens flaying means Jim Mallinder’s men cannot be caught at the summit and will have a home play-off semi-final against the fourth-placed side on May 23.
Lee Dickson and Luther Burrell both scored twice, with Ahsee Tuala and Jamie Elliott also dotting down to earn the five points needed to ensure Saints moved six clear of second-placed Bath.
That means they will head to Leicester next weekend knowing that whatever happens in the final game of the regular season, they will finish first this season.
And Mallinder made full use of his bench in the second half of the thumping win against Welsh to keep his players fresh in anticipation of sterner tests ahead.
Welsh had headed to the Gardens with a record of 30 defeats in as many matches this season, and they were under the cosh from the outset.
Saints bossed possession and territory, kicking five successive penalties to the corner in the pursuit of tries.
But Welsh were showing plenty of character, resisting relentless lineout drives to stop the home side opening the scoring inside the opening 10 minutes.
The visitors’ defence finally cracked at the sixth time of asking as the lineout drive allowed scrum-half Dickson to pop up and score.
Stephen Myler made the conversion to give his team a 7-0 lead after 15 minutes.
And with a dominant scrum, Saints were continuing to turn up the heat, but they were failing to make attacks stick at the vital moments.
That was until Ken Pisi gathered a high ball and turned on the turbos, speeding past the Welsh defence before offloading to Tuala, who used his muscle to power over.
Myler’s conversion made it 14-0 but Welsh responded with force, desperately trying to force their way over the line after kicking to the corner on a couple of occasions.
But Saints stood tall, turning the ball over, and they were soon at the visitors’ door again as a trademark rampaging run from Samu Manoa put them in position.
A scrum penalty saw Myler extend the lead from the tee, and he was also on target early in the second half.
But what Saints were craving was tries and after Ken Pisi and Tuala combined down the right, Dickson picked up to fly in for his second score of the match.
Myler missed, but with his team 25-0 up it didn’t matter.
And Saints soon set about securing the bonus point as some patient play eventually ended with Burrell bulldozing his way over the line.
Myler made it 32-0 with the conversion before Welsh forward Jack Gilding was sin-binned.
Burrell soon went over again, with replacement James Wilson adding the extras.
And there was still time for Elliott to score in the corner, with Wilson putting some added gloss on proceedings.
Saints: Tuala; K Pisi, G Pisi, Burrell (Stephenson 67), Elliott; Myler (Wilson 60), Dickson (Fotuali’i 56); A Waller (Corbisiero 56), Hartley (c)(Haywood 56), Denman (Ma’afu 56); Lawes, Day (Dickinson 60); Wood, Clark, Manoa (Fisher 60).
London Welsh: Jewell; Awcock, Reynolds, May (c), Elder, Barkley (Robinson 67), Rowley (Lewis 67), Trevett (Aholelei 62), Britton (Morris 50), Cooper (Gilding 50), West, Corker (Down 50), Browne, Waters (Liston 60), Fonua.
Referee: Andrew Small