Saints suffered yet another gut-wrenching late defeat as Saracens snatched the spoils at the death at Stadium MK.
The men from Allianz Park recovered from 25-12 down, scoring two tries in the final 11 minutes and landing the last-gasp conversion to seal a 27-25 victory.
Saints had led all the way until two minutes from time, when Marcelo Bosch charged over to add to Chris Ashton's earlier effort.
And Alex Lozowski, who impressed with the boot all afternoon, kept his composure to slot the winning kick.
It was yet another agonising defeat for Saints, who lost have now lost late leads against Bath, Leicester, Wasps and Saracens since February.
Jim Mallinder's men do move up a place to sixth in the table, one point above Harlequins, but that will be scant consolation after yet another game they could, and should, have won.
Saints had gone into the match at Stadium MK, which provided their home for the day, having won just one of their nine meetings against the current Aviva Premiership top six.
But they fancied their chances against a Saracens team without the likes of Maro Itoje and Owen Farrell.
And Saints were to get off to the perfect start as Stephen Myler put up a high kick and Pisi gathered superbly before offloading for the onrushing Mallinder to score.
Myler converted and Saints were soon on the charge again, with Mallinder kicking a bouncing ball ahead, forcing Saracens to scramble.
It was suddenly wave after wave of green, black and gold pressure, with Saracens really under the cosh.
And after Duncan Taylor was sin-binned for killing the ball, Myler slotted a penalty to make it 10-0 with the match approaching the 20-minute mark.
Saracens responded with a Lozowski penalty and Saints soon lost France star Louis Picamoles to injury, with Teimana Harrison his replacement at No.8.
Harrison was soon helping his side to push forward again, with Saracens forced to concede another penalty under pressure.
Myler kicked it to restore Saints' 10-point lead, but Lozowski responded again with another penalty of his own.
Saints were then hit with another injury worry as Myler was forced to receive some treatment, pushing Mallinder into kicking duties.
And the centre was to miss a penalty before the break, hitting the left post with his effort to leave the score at 13-6 at half-time.
Myler was forced off at the break, with Rory Hutchinson on in his place and Mallinder, who had been one of the stars of the first half, moving to 10.
But it was to be the forwards who got the second half off to a flying start, as hooker Hartley profited from a big lineout drive to score.
Mallinder landed the conversion and Saints had a 14-point buffer, but Saracens responded with another Lozowski penalty.
It wasn't long before the fly-half added a further three points as the men in red continued to chip away at the Saints lead.
But Saints were the ones playing all of the rugby and they were to score from another sumptuous move.
Tom Wood blasted a hole through the middle and fine work from Hutchinson and Tuala teed up Pisi for a try in the corner.
Mallinder missed the tricky touchline conversion, but Saints now had 25 minutes to find the bonus-point try that would cap a fine team showing.
But Saracens were to score next with former Saints wing Ashton finding space to cruise over in the corner after his side took a quick penalty.
Lozowski missed the conversion to leave the gap at eight points with nine minutes to go.
But the Saracens No.10 was soon making amends, landing a penalty that cut Saints' lead to just five points with as many minutes to go.
It was getting far too close for comfort and tension was to turn to despair soon after as Saracens counter-attacked and Bosch dived over.
Lozowski had to land the kick for the win and he was ice-cool, grabbing the points that were to spark scenes of celebration in the away camp at the final whistle.
Saints: Tuala; K Pisi, Burrell, Mallinder, Foden; Myler (Hutchinson 40), Groom (Dickson 66); A Waller (E Waller 68), Hartley (Haywood 66), Brookes (Hill 54); Lawes, Ribbans (Ratuniyarawa 71); Gibson, Wood (c), Picamoles (Harrison 25).
Saracens: Goode; Earle, Bosch, D Taylor (Tompkins 46), Maitland (Ashton 52); Lozowski, Spencer (H Taylor 66); Lamositele (Thompson-Stringer 68), George (c) (Brits 52), Koch (Du Plessis 52); Isikewe (Rhodes 56), Kruis; Conlon (B Vunipola 54), Burger, Wray.
Referee: Matthew Carley