James Grayson landed a last-gasp penalty as Saints secured a sensational 27-25 Gallagher Premiership opening-day win at Saracens.
Saracens infringed with 90 seconds of the match remaining and Grayson showed nerves of steel as he slotted the kick to secure victory for his side.
It was no more than Saints deserved after a display that contained plenty of spirit and no shortage of quality.
First-half tries from David Ribbans, Rory Hutchinson and Henry Taylor, against his former club, gave Saints a 21-16 half-time lead.
And though Ben Spencer continually stuck the boot in after the break, Saints kept plugging away and won the late shot at goal that allowed Grayson to give them the four points.
It was Saints' first victory at Saracens since March 2016 and ended a run of six successive league defeats to Mark McCall's men.
The signs had initially looked ominous as Alex Lewington carved Saints apart, helping to earn a penalty that Spencer kicked.
Knock-ons were costing Saints dear as they coughed up possession in the Saracens 22 and then on halfway.
And Saracens were able to apply pressure in the away half, with Will Skelton's gargantuan carries causing Saints all sorts of problems.
Spencer slotted his second penalty of the game to make it 6-0 before Saints started to knock loudly on the door after good runs from Taqele Naiyaravoro and James Fish.
But again Saracens forced the knock-on, ending a promising attack.
However, Saints kept coming and after Alex Coles almost scored in the corner, patience was rewarded by Ribbans, who dived over cleverly.
Grayson added the extras with aplomb and Saints led 7-6 after 25 minutes.
But Saracens responded immediately through another Spencer penalty and they soon extended their lead as Ben Earl's brilliant break was finished by full-back Matt Gallagher.
Spencer converted to make it 16-7, but Saints responded superbly, stealing the ball in the Saracens half and eventually sending it to Hutchinson, who delivered a top-class finish.
Grayson converted and he was soon doing so again after a sensational Saints score.
Saracens spilled the ball and Saints took full advantage, bursting forward from their own 22 as Grayson produced a lovely kick ahead, Tom Collins gathered, sped forward and then fed a tidy pass to the onrushing Taylor, who scored against his former club.
Grayson took his time over the conversion in front of the posts before landing it, sending Saints in 21-16 up at half-time.
And the away side came out flying in the second period, thinking they'd grabbed the bonus point when Naiyaravoro released George Furbank after a huge carry.
But the pass was deemed forward and Saracens breathed a sigh of relief.
Saints continued to come but again it was handling errors that were costing them another try.
Saracens were under pressure as Saints kept playing their ambitious game, but key passes just weren't sticking.
And Saracens made them pay with a Spencer penalty won at the breakdown, reducing the deficit to just two points.
Spencer was soon on target again after an offence at the lineout, putting Saracens 22-21 up, but Grayson responded.
Spencer immediately restored Saracens' lead after an Coles offence from the kick-off, but he missed another kick soon after, hitting the post.
Rotimi Segun looked set to wrap things up for Saracens with seven minutes to go, but the wing was forced to knock on by some desperate Saints defending.
Boyd's men were penned in with Saracens applying the squeeze in trademark fashion.
But Saints finally got out with some more slick attacking play and Saracens gave away a crucial penalty with 90 seconds remaining.
Up stepped Grayson, who placed the ball between the posts to earn his side a sensational success.
Saracens: Gallagher; Segun, Lozowski, Tompkins, Lewington; Goode (c), Spencer; Adams-Hale; Pifeleti (Gray 39), Lamositele; Skelton (Hunter-Hill 76), Isiekwe; Clark, Earl, Wray.
Saints: Furbank; Collins, Dingwall (Symons 62), Hutchinson, Naiyaravoro (Sleightholme 62); Grayson, Taylor; Waller (c) (van Wyk 54), Fish, Hill (Painter 65); Ribbans, Moon; Coles, Tonks (Eadie 70), Wood.
Referee: Ian Tempest