Not only because Leicester Tigers had won five successive games going into the east midlands derby clash.
Not only because Saints had lost five successive matches before travelling up the M1.
And not only because Northampton had been smashed 63-13 by Saracens just seven days earlier.
But the most amazing thing of all was the group of players Saints took to Welford Road.
One pundit said before the match that even if he was only betting a fiver, he wouldn't go anywhere near placing it on the men in the striking away strip.
Because a group shorn of experienced faces such as Dylan Hartley, Courtney Lawes and Tom Wood seemed to have little chance of competing with a formidable Tigers team.
Saints had a first 15 that included men who hadn't played a first-team game for months.
And they had a bench packed with players who had barely played a first-team game at all.
Of the entire 23, only Stephen Myler had ever sampled a Saints win at Welford Road before.
Yet by showing an incredible togetherness and so much will power, the team got the win they wanted, beating Tigers on their own turf for the first time since February 2007.
It was also a first league double against Leicester since the 2003/04 season and here we take a look at the heroes who secured one of the most memorable victories of recent times...
One of the few Saints starters who has been a fixture in his shirt number this season. The Samoan arrived at Northampton as injury cover for Ben Foden back in February 2015 and he has shed plenty of weight, working so hard to secure not only a longer-term contract but also a regular spot in the first 15 during recent seasons. He scored the superb try that eventually proved so crucial at Welford Road, sidestepping his way through the Tigers defence. Earlier, he had conjured up a fantastic try-saving tackle to stop wing Adam Thompstone scoring in the corner.
Still out of contract this summer, he could have played his final game for Saints at Welford Road, and having come so close to winning there on so many occasions, this will have been so enjoyable for the experienced back. He started the scoring for Saints, showing he's still got it with a fantastic finish, before producing a big display all around the park to help his team earn the win they so desperately wanted, banishing more than 11 years of hurt.
Was skipper for the day, but only managed to spend 12 seconds in the game as he was unfortunately involved in a horrible early collision that left him with concussion and an arm injury. Had to spend the weekend at Leicester Royal Infirmary receiving specialist care for the arm problem, but he will have enjoyed hearing about the other 79 minutes 48 seconds of the Welford Road success from his team-mates.
Had only been victorious in two of his 18 games for Saints prior to this match, earning wins against Harlequins and London Irish, so needless to say this will be his most enjoyable success by far. Has been unfortunate with injuries since joining the club last summer but is now getting a run at centre after initially being seen as a fly-half, and this will have tasted so sweet after so many defeats.
Looked like he might not play again for Saints after comments made by Alan Gaffney following the defeat to Sale in March, with the suggestion being that the Wales wing didn't want to play against the Sharks. But he has shown he is up for the fight since, getting stuck in and shedding blood for the cause here as he was briefly forced off after taking a big hit to the nose during the first half. He had turned 26 in the build-up to the game and this proved to be some birthday celebration.
Fittingly, his final Saints appearance at Welford Road finished the same way as his first: with a win. Myler, who joined Saints in 2006 and will leave this summer, was the only member of the 23 to have tasted a Northampton victory at Leicester and he made sure he shared that feeling with his team-mates, keeping his cool as he kicked everything that came his way. He racked up 12 points as he once again outshone England fly-half George Ford when it really mattered.
The South African scrum-half has been in and out of the team this season, battling with compatriot Nic Groom for a starting spot. But with Groom having headed home earlier this month, Reinach is very much first-choice now and he showed why, overcoming an early error by producing a superb display that encompassed a fine try and an even better assist, for Tuala's winning score.
The prop appears to be on his way out of Saints this summer, but he followed in the footsteps of brother Salesi by being part of a squad that earned a vital victory against Leicester. Ma'afu was a picture of fire and desire, putting in big hits and not being put off by the fact referee Matthew Carley kept calling him Salesi on the day.
Has not been able to play or train as much as he would have wanted of late due to a problematic injury, but he declared himself fit for derby day, replacing Reece Marshall, who had impressed against Saracens seven days earlier. Haywood was once again impressive, ensuring Saints didn't miss skipper Hartley, before being forced off during the second half for a head injury assessment.
An incredible showing from the prop, who has fallen out of favour at Saints this season but who got a start thanks to injuries to Kieran Brookes and Jamal Ford-Robinson. And how he took his chance, stepping up in a 66-minute showing that made him the man of the match in the eyes of many. He carried superbly, defended well and battled against Ellis Genge in the scrum on an afternoon to savour as the 23-year-old proved his point in the best style possible.
The Fijian lock arrived at Saints from Agen at the start of last season and has become a big favourite at Franklin's Gardens thanks to his friendly off-field persona and powerful on-field performances. Ratuniyarawa was at it again last Saturday, making a mountain of tackles and shrugging of a knock at the end of the first half to help his team secure a sensational success.
One of the stories of the day. The lock had only played once for Saints this season prior to this match, with his most recent appearance coming in the Anglo-Welsh Cup defeat at Exeter on November 4. Yet he had no issues slotting into the starting side at Welford Road and he delivered a fantastic display that once again reminded everyone of just how much talent he possesses.
Such a sweet success for the flanker against his former side and he even crowned his 150th Premiership rugby outing with the official man of the match prize after yet another indefatigable performance saturated with desire. He so often leads by example for this Saints side and will be a contender for the player-of-the-season prize.
Was making a rare start on the flank, having been employed as a No.8 this season. He had only been at seven once before during this campaign, lining up there against Gloucester back in October. But the switch worked for Saints as he was heavily involved in the game, playing a key role in setting up Reinach's first-half score and making so many big tackles and carries that rocked the Tigers on their own turf.
Had not started a game for Saints since the Champions Cup defeat at Saracens on January 20 and was making just his second Premiership start of the season, having lined up from the off against Sarries on the opening day, when he was forced off with an injury just 15 minutes into the match at Twickenham. Made up for lost time here, with a huge display that saw him carry the fight to Tigers time and again.
Will be leaving the club for Bedford Blues this summer, but with Hartley and Marshall both out and Haywood forced off for a head injury assessment, the hooker got his big chance, coming on and playing a key role in helping Saints to claim a win against a club at which he spent time in the Academy.
Had not played a first-team game since early December after breaking his arm against Newcastle Falcons at Franklin's Gardens. He got 40 minutes for the Wanderers against Newcastle five days before this game but showed no signs of rustiness as he came on and immediately won a scrum penalty against the head. He was later yellow carded for a high tackle, but returned to the field to help his team hold out late on.
What a 14-minute cameo from the England Under-20s prop, who has only just turned 20. He helped to win a huge penalty close to his own line when it looked certain that Leicester would score and he also had a big say in the scrum, too. The former Felsted School pupil was making just his second first-team appearance and it will be one he will remember for ever in what looks likely to be a successful career.
Looks set to depart Saints at the end of the season as his contract is up and he has not played as much as he would have liked, but he got a taste of the action in this game, standing tall after replacing the impressive Rayuniyarawa.
The Saints Academy product will be leaving the club this summer, but this was a great way to sign off as a Northampton player at Welford Road, making the most of back row injuries to get more game time as he helped to put years of Tigers wins against Saints behind him and his club.
Still only 20, the scrum-half wouldn't have been involved at Welford Road had Groom not left the club earlier this month, but he is certainly making the most of his opportunity and he kept his concentration to ensure there was no late heartbreak for Saints here.
Thrust into the action after just 12 seconds, this was some way to mark his comeback from a shoulder injury. The centre hadn't played at all since the defeat to Sale Sharks on March 3, but he was back with a bang, producing a dominant midfield display to help propel his team over the line.
The fans' favourite got two bites at the cherry on derby day, replacing North after the Wales wing got a bang to the nose during the first half and then coming on for Tuala in the second period. Collins has not been given the game time many would have hoped for during this campaign, but he again played his part in a big win against Leicester, as he did in May, 2014, when he started against Tigers in that memorable Premiership play-off semi-final success at Franklin's Gardens.