Saints made it a hat-trick of Welford Road wins in succession as they beat Leicester Tigers 31-22 on Saturday afternoon.
Fraser Dingwall led a fightback after Tigers had gone 22-14 up, with the talented centre providing a score for Tom Collins and then grabbing one of his own.
James Grayson, who kicked well all afternoon, put the icing on the cake with a penalty five minutes from time.
It means Saints have now won three games in a row at the home of their local rivals, having previously failed to win there in more than 11 years.
And it also ended Tigers' Premiership Rugby Cup hopes as they needed a win to boost their bid to qualify for the knockout stages.
Saints were already out of contention, having lost their opening three games, but the victory against Tigers comes as a huge boost ahead of next Saturday's Gallagher Premiership opener at Saracens.
Saints were up and at 'em early on at Welford Road, piling the pressure on a Tigers defence which refused to shift, delivering some huge hits and eventually forcing the knock on.
But Saints refused to be deterred and scrum-half Henry Taylor, who shone against former club Saracens last weekend, spotted a gap, sped through it and passed to the onrushing David Ribbans, who had run a lovely line to score.
Grayson added the extras and Saints continued to pour forward, showing no fear in enemy territory.
Tigers were being penned in, unable to relieve the pressure, and Taqele Naiyaravoro's offloading game was causing them all sorts of problems down the Saints left.
But the hosts were to land a sucker punch as Noel Reid turned defence into attack, chipping ahead, gathering and flinging a fantastic pass to the left wing, where Jonah Holmes was waiting to sprint home.
Reid failed to add the extras but his good work had put a spring in the step of his side and Saints were now the ones on the back foot.
Reid missed a penalty chance he would have expected to kick soon after as Saints just about kept their noses in front.
That was until Holmes found more space on the left and held off Ryan Olowofela to score his second try of the afternoon.
Reid missed from the tee again, but Saints badly needed to rediscover the early momentum that they had lost.
And they did just that thanks to Ribbans, who again powered forward with an unstoppable run and finish to give Saints their lead back.
Grayson converted to make it 14-10 and Saints were desperate to hammer home their advantage, twice kicking penalties to the corner.
But Tigers forced a knock-on from Andy Symons as Saints tried to piece together a move and the chance to extend the lead before the break was lost.
Saints again hunted for a try that would give them breathing space after the restart, but after hammering away at the home defence, they found Tigers tough to crack once more.
And they were made to pay as Tigers made their way up the pitch and after booting the ball to the corner, they rumbled over, with Will Spencer the scorer.
Reid again failed with a tricky kick from the touchline, leaving the gap at just one point, but he was soon extending it with ball in hand, sprinting in for the bonus-point score after some good work from centre Andy Forsyth.
Reid added the extras, to ironic cheers from his own fans, as he registered his first successful kick of the match.
Saints were now 22-14 down and they needed to produce a rapid response, having been stung by two quickfire tries.
But disciplinary problems were costing them as they were regularly punished for high tackles by referee Christophe Ridley.
That gave Tigers the opportunity to continually build momentum and Saints turned to their bench to try to help them get back in the ascendancy.
Tigers still looked the most likely to score next, but they were hit by a big blow as they gifted the ball to Dingwall and he made the right decision, executing well as he kicked ahead to allow the speedy Collins to chase and gather for the score.
Grayson converted to cut the gap to one point and Saints then sprung another surprise as Dingwall went from provider to scorer.
He flew through in acres of space and dived over in delight after picking up a Rory Hutchinson pass.
Grayson converted and Saints led 28-22 with 13 minutes to go.
Saints then did some strong defensive work and also excelled in the scrum, winning a penalty close to halfway as they sought to play the closing stages in Tigers' half.
The hosts gave away a needless lineout penalty, which allowed the nerveless Grayson to kick to make it 31-22 with five minutes to go.
The clock was against Tigers, and so was Saints' spirit as the away side shut down a couple of late attacks and celebrated with vigour as the final whistle was blown.
Leicester Tigers: Worth; Thompstone, Forsyth (Olowofela 72), Eastmond, Holmes; Reid (Hardwick 66), White (Harrison 68); Gigena (Leatigaga 48), Youngs (c) (Kerr 56), Heyes (Cortes 70); Spencer, Wells (Green 60); Liebenberg, Reffell (Boladau 17), Thompson.
Saints: Furbank; Olowofela (Collins 48), Dingwall, Symons (Hutchinson 59), Naiyaravoro; Grayson, Taylor (Mitchell 67); van Wyk (B Franks 52), Fish (van Vuuren 11), Painter (Hill 52); Ribbans, Coles; Tonks (Moon 59), Brüssow (Eadie 59), Harrison (c).
Referee: Christophe Ridley